Security Fasteners

As a lock collector, I'm also interested in security fasteners. It can be argued that these fall somewhere between locks and bolts/screws, that they are not worthy of consideration by lock collectors. Most are hardly more than modified bolts/screws, but some are very close to being locks (Raco/WRRS/SafeTran for example). Regardless of where they fit, here is a start at cataloging them.

A good place to start is the Wikipedia entry on screws. From there a 21-page US government publication was found on how to distinguish a bolt from a screw (the document has been revised five times so far).

Somebody else put together a nice summary of screws, see

Another good source of information is and its predecessor

Also which includes left-hand screws ("Opsit").


Also for another survey of screw drive systems. There is an interesting reference at the bottom to a publication "Assembly Technology Buyer's Guide" from The Hitchcock Publishing Company, Hitchcock Building, Wheeling IL 60188 but I can't find the company or the publication. I did find one reference that Hitchcock may be part of Capital Publishing/ABC Inc (or is it Capitol) but I can't find that either.

A good book might be Carrol Smith's Nuts, Bolts, Fasteners and Plumbing Handbook, published by Motorbooks International. It apparently includes information on how to obtain the above book from Hitchcock in an appendix, but I don't have either book.

Endeavour Tools in Australia has a catalog of security fasteners here, including several I had not seen before. They seem to "own" some varieties. has no images but does describe a wide variety of screws. It's pointed out here that a relative of the Phillips is Frearson, also known as Reed and Prince. However, the web site has disappeared; a 2011 copy is at

Bryce Fasteners has a set of truly unusual styles, primarily their "Key Rex" system.

Lara Specialty Tools listed a wide variety of unusual screws and drivers. However, around April 25, 2008, their web site started to come up with blank pages, pages not found, yet some pages still worked. It appears they have gone out of business. Some content is preserved on, starting for example here:, and relating to screws:

Barnhill Bolt has a few security fasteners and tools. was the first place I found detailed information on the Kinmar design. They are now

Southco makes latches which are used on electronic equipment racks, recreational vehicles (including boats), and even large trucks, with a wide variety of head styles. One of their main product lines is the E3 series, the catalog is at Another product line is the E5 series, the catalog is at Related engineering drawings include and

Camlock Systems makes various products that are similar to Southco, above.

iFixit makes tools and kits aimed largely at electronic devices such as cellphones and laptops.

Avsafe: Let's start with a no-slot screw, the Avsafe by Avdel Corporation. An oval head with no slot. Another variant is the "oval pan head security screw" for example from, here. There's almost no information at all on this fastener, and even the Avdel web site, now part of Stanley, doesn't mention them. My best guess is that they are no longer made by Avdel under the Avsafe name but if you do a Google search there are still a few places that sell Avsafe screws and drivers such as

The name was trademarked in the US in 1983 but was canceled on April 10, 2004.

Carriage bolts may not be designed for security or tamper resistance but they can be fairly effective in that role if the nut is difficult to access.

Not really a security fastener, but Pozidriv bits are often sold in sets of security bits. This is an offshoot of the common Phillips style but better suited to higher-torque applications. Driver sizes are numbered 0 (smallest) through 5 (largest). See for example:

The name Pozidriv is trademarked by the Phillips Screw Company from 1960 and is still an active trademark.

Combo: A combination Phillips and slotted, rather common if you look around. According to Lara Specialty Tools ( you should not use either a Phillips or flat driver, instead you should use a driver that is specific to this form. I didn't know that, I thought the whole purpose was in fact so you could use either type of driver.

Supadriv (sometimes incorrectly spelled Supadrive): Spotted on but their image (first, above) is quite poor and the description is almost non-existent.

A better image is on Wikipedia.

The Wikipedia article on pozidriv states that Supadriv is very close to pozidriv but slightly different in a few details.

"Supadriv" was trademarked in 1981 by G.K.N. Screws & Fasteners Limited in the UK, last owned by European Industrial Services (Fasteners) Limited and canceled in 2002 (though two other registrations were made in 1982 by the same company, and likewise canceled in 2002). Nevertheless I have found references that suggest Supadriv is trademarked by Trifast Plc. Perhaps true but not in the US?

Robertson (square): Not really a security screw but the drivers are not as common in the US as ordinary screwdrivers. Named after their inventor, they date back to around 1908. Robertson screwdrivers are supposed to have color-coded handles that correspond to the size. The size of the driver is designated by numbers ranging from 00 (very small) to 3 (rather large). They are a little rare in the UK and USA (though I've seen deck screws with square drive) but common in Canada (Robertson was Canadian). Naturally there is a tamper-resistant variety as well.


In the US, the Robertson name (as it applies to screws) was trademarked by Robertson Inc., Ontario Canada in 1974 and is still active.

An example of an external square drive is this latch from Southco. Similar products are made by Camlock Systems.

Quadrex: A combined Phillips/Robertson drive sometimes seen in woodworking. Not a security fastener, just unusual. US trademarked in 1984 by Isotech Consultants in Toronto, the trademark is now owned by either JCM Holdings (Indiana) or NLW Holdings (Alabama). Some web sites claim Quadrex (and Quadrex Plus) are tradmarks of Quadrex Consulting which is weird because they do trade consulting in Istanbul.

The Quadrex Plus adds a slot so that standard tools can be used if necessary. See US patent number 5,020,954 (the inventor was Geoffrey Dreger) which was granted in 1989 and assigned to Intools Limited in Ontario. On a Lord and Sons web page (now gone, try this instead) it is explained: "Quadrex (tm) is a licensed recess, originally developed in Canada. As a dramatic improvement over a Phillips recess, it provides multi-point contact with the driver bit and incorporates four perpendicular contacts. The benefit is a driver-recess combination without the cam-out action of a Phillips. Screws can be driven at severe angles and still maintain contact of driver and recess. Additionally the life of driver bits is prolonged, recesses are not stripped out, and the coating within the recess is not abraded to the extent of a Phillips drive."

Triangular bits are also weird enough to qualify loosely as tamper-resistant. I believe these are also called Tri Lobe, e.g. on Endeavour's web site here (though they have the wrong image on their driver page here), and they are also called TP3.

Triangular recess: These appear to be different than the Tri Lobe, above, in that the sides are straight rather than curved. According to Lara Specialty Tools (link dead, try instead) these are usually seen in die-cast scale models such as toys and model cars. Also seen in the Roomba robotic vacuum cleaner, and the Master Speed Dial padlock (early units used Phillips-head screws). Sizing is inconsistent, with some sellers stating the size (in millimeters) of one side, while other sellers state the height (flat side to apex) of the triangle. And like most others, available in tamper-resistant form with a center pin.

Tripoint: yet another unusual design used on electronic devices such as cellpones and laptops.

Tri-Wing: touted as tamper resistant and high torque. See:

One of several three-lobe shapes.

Size designations are just numbers, 1 being small and larger numbers corresponding to larger drivers.

These are used on Nintendo games. Also some digital devices such as Sony TJ27 and TJ32, cell phones, and no doubt other related items. Also used on some aircraft such as the DC-9, DC-10, and Boeing 717 where titanium screws could be damaged by conventional drivers with cadmium in the alloy (cadmium causes deterioration and fracturing in titanium), the three-lobed design makes it impossible to use conventional drivers.

The name Tri-Wing is trademarked in the US by the Phillips Screw Company from 1960 and is still active.

Another 3-lobe design. See (now gone, try instead). Note that DiyGear called this a Tri-Wing which is a term also used for the straight-legged variety. Belzer was a German tool-maker until it was acquired in 1988 by Bahco, but this still remains a mystery bit that can't be found so far.

This looks like it came from US patent 5,598,753.

Mortorq: US patent 6,367,358 (assigned to Phillips) describes a slot/driver based on the geometry of a spiral. This was developed under contract with the US Air Force. These seem to be what Phillips calls their Mortorq, here, which are even described as having low acoustic and radar return (i.e. these are "stealthy" screws). The actual patent is interesting because it goes into some of the mathematics of how a driver interacts with a recess. Earlier US Patent 5,957,645 appears nearly identical. The name Mortorq was trademarked in the US by the Phillips Screw Company in 2002.

Phillips also has a system they call Mortorq Super, possibly US patent 7,293,949 and/or 7,255,522

Sentinel: Resembles the Mortorq, above, except here the goal is a one-way screw. Found at and with the description "Sentinel (tm) - The original Nettlefolds one way pozidrive security system. This recess is ideal for easy and fast application with power tools. The most popular permanent option. No specialist tools required. Uses standard Pozi or Superdrive bits or drivers."

Torq-Set: Another unusual shape from Phillips, offering tamper resistance and high torque. Used in aerospace and military applications, observed on the SR-71 aircraft for example.

Size designations are just numbers, 1 being small and larger numbers corresponding to larger drivers.

The name Torq-Set is trademarked by the Phillips Screw Company, from 1960. Also 1978 and 2002.

Clutch: The goal does not seem to be tamper resistance, as a simple flat-blade driver should work well. Instead, these are presumably designed for industrial assembly where the driver should not slip out, unlike a simple slot. I did find a reference on eBay that they existed at least as far back as 1939, being used on Chevy trucks (and some cars) at least as recently as 1966 or even 1972.

Size designations seem to be literal such as 5/32", 3/16", 1/4", 5/16" and undoubtedly others; this is the long dimension. I don't know if metric equivalents exist.

There are two varieties, clutch "A" shown first above, and clutch "G" shown second.

Double-bitted: This looks like a clutch "A" (above) but much larger, with a pin in the center to make it more tamper resistant. These are seen on Rittal equipment racks, and latches made by Southco and Camlock Systems. There are two pin sizes, 3 mm and 5 mm. The Rittal part number for the 5mm key is 2531.000; for Southco E3-2-1 (3 mm) and E3-9-1 (5 mm). At first glance it might appear that the 5 mm tool will work 3mm fasteners because the central hole would merely be oversize, but according to Southco's drawings the bits are longer on the 5 mm tool and thus might not fit (see their drawing J-E3-2-1.pdf). However, if the bits are reduced by 1/2 mm on each side, the result might be a single key that works both sizes.

There is also a possibility that one of these keys might fit some cable-TV junction boxes if one of the bits is removed (in which case it might still function in a double-bitted lock as intended, as well). Pictures of Channell "P" keys look similar but no further investigation has been done.

Secure Phillips: Even the common Phillips can become tamper-resistant by adding a pin in the middle. The pin rejects tools without a corresponding hole in the driver.

Security (tamper resistant) hex (or Allen): A standard hex socket with a pin in the center which will block a driver unless it has a corresponding hole. On occasions the pin might be slightly recessed which will allow a standard wrench enough grip to operate.

Size designations are presumably the same as for non-security hardware, namely the literal size across the flats of the wrench (3/16", 2.5mm, etc.).

Another way to secure an ordinary hex socket is Endeavour's pin plugs (here and here) which are driven into the socket and render it non-removable.

Spline: Designed by the Bristol Wrench Company this style is well suited for high torque applications but is not frequently seen. Some have 4 lobes, others have 6 lobes. Just looking at one, if you don't realize it is a spline drive, it is easy to mistakenly use or try an Allen driver and thus deform it; this might be one reason for its rarity.

There is a variant of the Bristol spline (at least, it looks like a Bristol spline) with a pin in the center to reject drivers lacking the corresponding hole. However, these cannot be found and the picture may be fictitious or may be of a different style than Bristol.


Torx: Not really a security fastener, but when they were first introduced it seemed that way because drivers were hard to find. Torx was developed by Textron Fastening Systems (web site no longer exists) which apparently is now Acument Global Technologies.


See also:

Sizes are designated by the letter "T" followed by a number which gets bigger as the size increases, for example T2 is very small and T35 is much larger.

TTap: Described as being similar to Torx but with less wobble during installation. See, for example, which states the driver has a standard Torx tip with an additional conical extension that mates with a cavity in the TTap screw. There is a web site

Line Head: A collective term for two basic styles, one looks a lot like modified Torx (plain, top, and security, bottom) (except the points are sharper/narrower) and one looks a lot like Tampruf (below) but with 6 facets instead of three. These are used on Gameboys and other electronic products. Sometimes these are called "System Zero". The external variety have designations like ALHx where x=2 through 6. The internal variety have designations like ALRx and the security style of these are designated ALRxT.

See for example:

Polydrive: Looks a lot like the Line Head, above, and may in fact be the same. According to Wikipedia: Polydrive, also known as RIBE CV or simply RIBE, is a fastener specification. It is used primarily in the automotive industry. A polydrive bit has 6 teeth at equal spacing and with flat tips to the teeth. Size is determined by diameter at the star points... it resists cam-out, and is thus used in higher-torque applications such as brakes and driveshafts. A nut and bolt FAQ at states: This bolt is no longer in common use but will be found on older brake assemblies and body connecting bolts. Size is determined by point to point of the star points. Common sizes are 5, 6, 8 and 10mm.

Unknown: Textron (now Acument) patented a tamper-resistant design similar to their external Torx except it only has three lobes. US Patent 5,378,101 (filed 1992, granted 1995, inventors Gregory R. Olson and Clayton A. Allen) describes it as being more suitable for very small screws where Torx is difficult to form either as screw heads or drivers. These have not been seen in real life yet.

Cinstar: A variation of sorts on Torx Plus (5 points), found on Endeavour's web site here. "This is a proprietary design/trademark owned by Endeavour Tools. Due to the higher security level of this recess, Endeavour Tools reserves the right to restrict sales to 'approved' users. All users are recorded in a security register."

One review/description is on

Curiously, the name Cinstar was trademarked in the US (image, above) by Endeavour in 1999 but was canceled in 2002.

Tri-Circ: Listed on Endeavour's web site here.

Also listed on their driver page here as "Tri Lobe" which I believe is an error, the Tri Lobe shape is different.

Key-Rex: A proprietary system from Bryce Fastener. There are many minor variations such that a customer can have their own particular Key-Rex.

Keyed-Lok: A proprietary system from Bryce Fastener. Like Key-Rex (earlier) there are many variations so they can be exclusive to a particular customer. However, the name now appears to be used to describe a family of fasteners (Key-Rex and Penta-Plus) rather than the specific style shown above and the original line may have been retired.

Penta Plus: The name, at least, is trademarked by Bryce Fastener. I don't know if they own the design or just that name.

Bryce Fastener markets petagon-socket nuts and drivers.

Herz: A proprietary design from Endeavour here and here. "Herz security screws are a high security/proprietary design. These screws are available by special order only."

Scrulox: An 8-point design, not quite as weird as it seems. Apparently you use square Robertson drivers, the extra set of points must be there simply to allow easier engagement. According to Lara Specialty Tools (link dead, try a tamper-resistant style with a pin exists but is so rare they can't find a manufacturer. However they suggest a corresponding Robertson drive should work, just like the non-tamper-resistant variety.

12-point designs come in several specific styles but the distinctions are sometimes not spelled out by manufacturers or retailers.

Lara Specialty Tools (link dead, try instead) refers to these as spline drive, stating that 8-point designs are sometimes called spline but the name really refers to 12-point designs. They also state these are used on some Volkswagen cars which would point more specifically to the XZN below.

One 12-point style is the triple square. Borrowing heavily from Wikipedia: They are commonly found on German vehicles such as BMW, Mercedes, and Volkswagen. These screws are used in high torque applications such as cylinder head bolts and drive train components. Triple square bolts are common to early Porsche and Volkswagen constant velocity joints. Common sizes are 6, 8, 10, and 12 mm. Triple square drivers can be purchased at auto parts stores and through automotive tool distributors. Increasingly, triple square screws are found on other European and Asian makes of cars. Other names for triple square screws and drivers are "Double Hex", "Double Allen", and "Aircraft Screws". Despite this, "Double Hex" and "Double Allen" are misnomers. The recess in these bolts is actually (as the name suggests) made of three squares, not two hexagons. The corners are 90 degrees, not 120 degrees and therefore an Allen key will not fit them properly.

Although Wikipedia claims the XZN geometry used in some applications is a triple square, it may actually be a double hex (below).

Double hex is also a 12-point design but the corners are 120 degrees, not 90 degrees as with the triple square. Standard hex wrenches are said to be compatible though one might expect a lower torque limit before something starts to deform. There is some confusion whether "XZN" refers to triple square (which is what Wikipedia is claiming) or double hex (which is the claim on Based on appearance and the equivalence of a six-sided tool, I tend to believe XZN is double hex.

Shown above is a VW transaxle drain plug, which is also a tamper-resistant style, and a corresponding tool. These are sometimes described as 16mm, sometimes as 17mm; it is not clear if these are the same or if there are really two sizes. According to eBay seller "zdmak" the VW part number was 3357, now called XZN 16. Also used on the Porsche Boxster, Audi A4-A6, and VW Passat. An appropriately-sized hex driver might work if the pinhole is also correct, and a few VW tool/part vendors make a 6-sided tool as their model 7029, shown above. But one might expect a lower torque limit with a 6-sided tool, before something starts to deform, compared to using a 12-sided tool.

Spline drive is described on Wikipedia to be distinctly different from triple-square in that spline tips have 60-degree angles while triple-square tips have 90-degree angles. Double hex tips are 120 degrees, so the three are incompatible. Spline drives are given by numbers, #5 being one common size.

Dodecagonal (12 points): bits are for sale as part of certain sets on eBay, with designations like M5, M6, and M8. It is not clear if these are triple square, spline, or double hex.

12-point bolts and nuts are a little weird, and are not really tamper-resistant but here they are anyway. The Simi Fastening Systems model VCB205 bolt states "Installed & removed with standard 12 pt. socket wrench" on their web site. The main selling points seem to be higher torque and lower profile (if clearance is a problem).

A very common screw, designed so an ordinary screwdriver blade can turn it one way, but not the reverse. There are three sizes for the Un-Do-It tool: model 804, for #6 and #8 screws; 807 for #10 and #12 screws; and 810 for 1/4-inch screws. Simi Fastening Systems has a tool, model VCT238, which has this description: "A special screwdriver with two tungsten carbide tips mounted at a back angle to engage the sloping surfaces of a one way recess to remove the screw quickly and non-destructively." The name Un-Do-It was trademarked in 1976 by Robert A. Ross. A similar design is/was used by the German lock company Kromer for example to affix keyhole cover plates to safe doors.

This is the Eazypower "Get It Out" tool for removing these one-way screws. Reviews on suggest it does not work well. It also requires a certain amount of clearance around the screw's head, which the Un-Do-It (above) does not. Covered by US patent 6,047,620.


Spanner: Requires a two-point (or multipoint) spanner bit. The security comes from the simple fact that an ordinary screwdriver will not work. In the case of the nut, an ordinary wrench/socket is useless. These are sometimes called "snake eye spanner" screws if the spanner holes are completely inside the head, or "notched spanner" if they are at the very outer rim. Another name is "pig nose" or "pig nosed".

Some size designations are just numbers, 1 being small and larger numbers corresponding to larger drivers.

One variant has 4 points, seen here on the TR Fastenings web site as one example.

Another variant has 3 points (spotted on a computer monitor) but no images have been found to add here.

An interesting three-point head was spotted at with an image of the driver at

Tampruf: Rarely seen, though I have a Mosler Defender time lock that uses these (last image; and I made my own bit before I knew what they are!). The screws on my Mosler Defender appear to have a much more shallow angle than the other images shown above, so there are different (incompatible) versions on the same basic theme. See:

Is this what Barnhill Bolt calls their "Tri-Groove" tool?

The rather simple-looking stamped tool is pictured on this web page from Lucasey Mounting Systems.

The Tampruf name was trademarked in the US by the Jefferson Screw Corporation of New York in 1972, and was transferred to the Allegheny Bolt & Screw Corporation of New York (they have moved to California since then).

This may also be known as Trident, for example on the Tanner Bolt & Nut web site.

Above, Bell Automotive sells tamper-resistant screws for license plates which work on the same principle, though in this case with 4 grooves instead of 3. It looks like the straight-walled base would allow pliers to grip the head, allowing removal without the tool. The conical section should continue non-stop to the base.

Above, replacement cleats for athletic shoes bear a resemblance to Tampruf, though of course in this case tamper-resistance is hardly the issue. Two different tools are shown.

Kinmar: An unusual style seen on the Fastenright web site here (note, as of early 2015 they show the same driver image for both the permanent and removable styles). Also, and and A Google search will come up with many more images.

Scroll nuts/bolts: vaguely resemble Kinmar (above). See and, which includes the description "This high security nut is virtually impossible to remove without the unique matching driver. Due to its rounded design, there are no sharp angles to provide grip for normal hand tools. Suitable for medium to high torque applications. Requires special matching driver socket (all Scroll drivers are registered with a number and logged for added ownership security). Manufactured in A2 stainless steel." These may be the same thing that Fastenright calls Wave Nuts and Wave Bolts here.

A cross-shaped latch, and matching key, found on some types of freezers.

Pentagonal (external): These are found in the US on water meter boxes, main water line valves, and on fire hydrants. See also Penta Plus, above, for recessed pentagonal screws and nuts.

Pentagonal-headed bolts can be used for securing manhole covers, such as those available from GMP Tools (see also Naturally GMP also sells wrenches, which are also available from Craftwork Tools, see here and here.

On a smaller scale, pentagonal bolts and sockets are available from Bryce Fastener.

Smaller still, one common style of freezer "lock" uses a pentagonal shape, sometimes with a part number of D8591.

Pentagonal fasteners are also showing up in automotive applications such as assembly of dashboards and brake calipers (next two images).

A 5-lobed Torx-like fastener is used on some electronic devices. This might be the Apple Pentalobe Security Screw (second image) ( or a 5-point Torx-like fastener (or both might exist). The third image is from iFixit and may represent the actual shape with the other two being common misrepresentations.

Triangular (external): Here's an example of a large external triangular style, in this case on water hydrants in Austria, according to about halfway down the web page.

The second image is an equipment latch by Southco.

The third image is of a freezer key that is triangular and appears to be much less common than the pentagon or cross types shown above.

3-Lobed (external): Another design found on water hydrants that may not even have tamper resitance as a goal.

The Channell company,, supplies equipment to telephone/cable/television companies including outdoor enclosures for cables. These boxes often use an interesting locking device which needs one of the drivers shown above. They seem to range from 5 points to 8 points. Two different 5-point tools are shown above, the left one centers itself on the outside rim of the "nut" while the second one (three different images) centers itself via the center pin and a hole in the middle of the nut. The pin styles seem to be Channell originals, while the rim-centering style may be made by a company called Diversified Control Incorporated ( (and they might have done this to avoid patent infringement). The last image is of an 8-point "nut".

Southco makes latches using the 7-point configuration, but this only shows up in their drawing J-E3-10-3, not in their catalogs. They refer to it as a "flower recess".

They seem to come in different configurations, some being symmetric and others being asymmetric, and so on. Sellers want way too much money to just start collecting them all!

It might be possible to make a single-point tool (plus the center pin) to open these, but it might be difficult to make such a tool with enough strength, depending on how stiff the lock's spring is.

A similar idea is used by the Knox Company on their locking standpipe/hydrant caps. These appear to use a 7-lobe configuration (larger than those shown earlier), and no central hole. More is disclosed in the various Knox patents.

McGard started making wheel-locking nuts in 1966 using a pattern similar to the Channell units above (McGard may even be the manufacturer of the Channell units). The lug nuts and other fasteners are sold in a variety of patterns. McGard has branched out into a number of fields such as marine applications and meter protection. They also make a spline-drive lug nut (above) which strongly resembles US patent RE33,114 which is a re-issue of US patent 4,616,535.

A patent search for the word "McGard" as assignee will yield many designs.

Other companies manufacture similar products.

DS Series: found on Endeavour's web site here with these warnings:

So it looks like they pay writers to say the same thing over and over but slightly differently each time.

4 Hole: This looks like a cross between the DS (above) and a 4-slot spanner, found on the Fastenright web site. See also and which includes the description "This security nut is for low torque applications and is manufactured with a narrow circular groove above the small locating holes, rendering this nut tamper resistant. This aesthetically pleasing head design is often specified purely for its good looks, particularly on glass panels and stainless steel architecture. Requires special matching driver socket. Manufactured in A2 stainless steel."

Tubular latch: Made by Southco. At first these look like oversized Ace-style pin-tumbler locks. But in fact they are simple latches, sometimes used on electronic equipment racks, and some Recreational Vehicles (such as Fleetwood). One style has 4 notches (long-short-long-short) and is Southco part number E3-5-15. The other style has 3 equal-sized notches, Southco part number E3-26-819-15. No others are known to exist. It might be possible to build/modify a key to operate either style, by machining a single "notch" in the key that spans nearly the entire circumference.

Armour Rings: From Endeavour, here: "Armour Rings are ideal for securing already fastened Hex bolts. Armour Rings can be tapped into position on either the bolt or the nut using conventional tools. Once fastened, Armour Rings cannot be removed."

But on the same web page they also say "Armour Rings are designed for securing already fastened Hex bolts, and importantly, do not effect the torque values already present in the Hex fastener. Armour Rings are not removable using conventional tools." This begs the question, what sort of unconventional tool does in fact remove these or was the writer dreaming of approaches such as welding sloped tabs onto the ring to allow removal with a wrench?

This 32-point knurled and tapered nut is from Simi Fastening Systems, for example here as their model VCN175. They also sell a corresponding tool for installation and removal, here, as their model VCT191 (because all three thread sizes on the nuts are the same external 1/2-inch diameter, one tool operates all three nuts).

Shear nuts and bolts, e.g. from Endeavour here, Fastenright here, and elsewhere.

The first image, above, is the drawing from US patent 5,120,168.

One trade name is Vandlgard, trademarked in 1978 by VSI Corporation but that trademark has expired. These are driven like a hex nut/bolt but the driving element then shears off leaving a conical-section (frustum) nut that is very difficult to remove (similar to Armour Rings, above). Assuming there is enough of the bolt sticking out of an installed nut, removal can be facilitated by a second nut (see also Tufnut below), as described in a US Department of Transportation document here on page 13 (which is page 16 of the PDF file); it might be possible to remove one of these by screwing on a standard nut and using the vise-grips on the conical section.

Similar products are offered by Simi Fastening Systems and TR Fastenings.

Tufnuts, which seem tough until you read the directions (from Allstate Sign & Plaque Corporation). It might also be possible to facilitate removal and/or installation using a standard nut (possibly with a large washer) on top instead of a second (temporary) Tufnut as shown in the instructions.

Woodsert: Not a security device, but it is a little weird. This has a wood-screw outer thread and a machine-screw inner thread. So it's really just an adapter to allow machine screws in wood. But the tool is just barely odd enough to include here.

The NoGo is a shield that surrounds a nut or bolt-head to prevent access. It looks almost permanent except one could possibly drill a hole in the center, tap it, and pull it out; but not easily. This was found on the Fastenright web site. See also Insight Security.

The above is an image from an eBay auction in 2006. It shows one style of fastener, and below that the corresponding tool and a tool for a different style not shown. Exactly how the shown fastener is supposed to be used is not clear; these may be what are called barrel nuts or barrel screws.

These could be viewed as "anti-security" screws. The first example can be driven by a flat-blade screwdriver, a Torx T-15 driver, and is easily turned by fingers. It also can be driven by a 12mm socket though this is probably not by design. This one came off a Dell computer and is threaded as #6-32. The same idea is used on Brooks power-meter rings such as their Handi-Ring (product number 10-9090) which can be finger-tightened, and can accept a slotted driver or 3/16-inch hex drive.

Utilco makes hardware for power distribution which includes the following enclosure "locks":

Not much information other than their web site explaining "Shear head screws providing safety and tamper resistance" so apparently the installer should tighten these until the head separates. Removal is then only possible by cutting the "shackle" so this is clearly something they don't anticipate a need for very often. Compare this practice with transformer boxes and other enclosures which are locked up with nice Wilson Bohannan or Herculock brass padlocks. The tradeoffs are security versus tamper resitance/evidence, and whether the enclosure is accessed rarely (in which case the cost of replacing one of these cheap "locks" is low) or more frequently (in which case a padlock pays for itself by being re-usable).

One style (Figure 3, above) is available from, here.

Utilco is a division of Ilsco.

Herculock also markets a one-use breakaway lock, shown above. This again raises the question, who actually manufactures them?

Engineering Unlimited also makes similar "padlocks" via their Sterling Security Systems division. These disposable locks are described here; at one time (mid 2008) they claimed a price of 86 cents apiece in "small quantities". You can see the tapered body of the hex-head screw, intended to break off when tightened.

Another "padlock-like" seal is made by Dickey Manufacturing Company. The loose end of the cable is secured by a screw in the side of the body, which then breaks off (along with the wrench; it's all one piece to begin with) when tightened.

Similar products are sold by TydenBrooks and Smith Flow Control.

Screw Locks: These were (and still are) used by railroads to lock low-worry items like battery boxes. In the images above are samples from RACO (Railroad Accessories Corporation), two different styles from Safetran, and one from WRRS (Western RailRoad Supply). They require nothing more than a wrench to unlock; most use a hex socket wrench (though two different sizes exist, 1/2" is very common), but some use a triangular wrench (again, two different sizes exist), some a spanner (and most of these have a hex-head with slots for the spanner), and a rare variety uses a modified "D" shape. The triangular and "D" styles were sized so that one size of Imperial (fractional-inch) socket wrench would just spin, and the next-smaller size would not fit, but this good planning is thwarted by Metric sizes which are in between and seem to work OK.

SACO (Signal Accessories Company) was formed in 1906, their locks used a cast iron body with a brass screw. SACO became RACO, Railroad Accessories Corporation, in the 1920s based on patent records (the earliest being 1,437,287 filed in 1920) and advertisements. On Google Books, for example: (1970) describes RACO as Railroad Accessories Corporation. The lock was covered by US patent 2,079,578 which was filed in 1934 and granted in 1937. In 1970 a company abbreviated CCI acquired most of RACO's capital stock. A Google Books snippet view at suggests that Safetran was created in 1971 to acquire two CCI companies, possibly including RACO, though the snippet view is inconclusive. The proceedings of the IEEE Vehicular Technology Conference, volume 2 (1985) page 295 states that MIPCO had merged with RACO to form Safetran, which was owned by CCI. Safetran rail products were acquired by Invensys Rail Corporation which was then acquired by Siemens Mobility Division; they do not appear to make locks. An archived catalog entry, Section K (Track and Circuit Hardware), subsection K-6-2, is here (two pages).

WRRS went through many changes and is now part of Western-Cullen-Hayes, the history is here. But they no longer make screw locks.

Inner-Tite Corporation manufactures a line of meter seals and locks for revenue protection. The first two images show their tamper-resistant screws/nuts and two styles of corresponding tools.

The next two images show their padlock and one style of keys. When first observed, it appeared it was just a fancy screw lock, but the keys and description confirm it's a real padlock and seems to use a mechanism similar to Abloy's.

Another tamper-resistant device for electrical meters is the Jiffy Lock from Inner-Tite, here. There appear to be at least two different styles.

Several companies make electrical meter lock rings that require a special tool for removal. These include:

Similar tools appear on eBay for unlocking some Channell communication boxes. They appear to operate by reaching through a hole, latching onto a locking element, and pulling outward to unlock. Extra security involves the use of a central pin that must be held and moved relative to the locking collar, varying the lengths of each, and other measures. Some of the prices these tools fetch on eBay are amazing.

The basics of the barrel lock are described in US patent 1,923,025 from 1933, and many related patents. Some others include 3,002,368 and 3,033,016. Try a search on these patent numbers to find other, related, patents.

A really unusual 5-dimple nut used for interconnecting batteries on a modified U.S. Electricar S10 pickup truck. The nuts seem to combine elements of the Kinmar (rounded head) and Inner-Tite (ball recesses; or are they conical?). In fact they look very much like the Kinmar re-usable nut shown earlier (but it's a poor image of the Kinmar) except the Kinmar recesses don't seem quite the same. The batteries are sometimes referred to as BB600 cells (a generic military designation, not a particular manufacturer's part number; BB600A/A is a similar battery but uses a different plate separator) and are wet nickel-cadmium cells built for aircraft use (OK, military aircraft, that explains it). Apparently the cells have 10-32 threads and for the military studs are installed that have 3/8-inch threads on top. Another suggestion I ran across was to stick ball bearings into the dimples with grease, and then try to find a hex socket of some size that just happens to get a good grip (or use the Sears Gator-Grip socket); I did not run across any story of this working. Yet another suggestion was to make a sort of C-spanner wrench with two points properly spaced; again, no reports of success (or attempt). The person who posted these images on the rotordesign web site made his own tool on a CNC milling machine, wood was used as a test material before cutting metal. The web site is not well organized, try which is a directory listing but contains many images of the batteries, and under the "bb600socket" subdirectory there are images of how the tool was constructed.

Sargent and Greenleaf makes what they call the Environmental Padlock (so named because it survives harsh environments). Here we see the top-mounted cylinder-locking nut which is sort of a lopsided spanner. It is unknown what a real tool looks like for one of these. It doesn't seem likely that the design is intended to make it more secure but why did they make it like this? On some of these locks the nut is secured with a roll pin so there is no non-desctructive way to take it apart; it's assembled in the factory, and that's that. Others use a setscrew that is accessed only when the lock is open and these locks could be serviced or re-keyed in the field (is that common or rare, or is the intent for factory-only servicing?).

Two different diameters for the outer hole have been observed.

Abloy uses a slanted 4-facet design on the cylinder retaining nut on some of their padlocks (2-facet nuts have also been seen). This is probably not a security feature, just a manufacturing detail. A "proper" tool for this has not been seen. Locksmiths probably just use a screwdriver. So I built my own tool.

Shielding bolt heads from easy access is a simple way to resist tampering. Here a conical piece of aluminum is sized so that a standard socket wrench (1/2-inch in this case) cannot be used. Thin-walled sockets are available in stores but even those might not work. A special very-thin-walled socket is probably available for this purpose. The manufacturer and brand name of these are unknown. They are found on some traffic signs for example.

Similarly, telephone-company junction boxes often use a hex-headed screw which is shielded as shown above. In this case a 7/16-inch socket wrench works fine though there are thin-wall "can" wrenches specifically made as well, such as those by Jonard Industries Corp, here.

American Casting and Manufacturing Corporation makes several lines of security seals, though none of them quite fit the intent of this web page. is a DOD manual on security seals for domestic cargo.

poiexc23vf0 is a unique tag so I can see if this page gets discovered by Google.