Everything you never knew you needed to know about Recessed Screw Drives
October 2010 | Filed Under: Resources
Security Screw Recesses
Security screws have often worked on the principle of ‘Obscurity is Security’. i.e. if no one can get hold of the driver, no one can undo the screw. Unfortunately the internet and the global market place has changed all that. It is now possible to buy driver bits from all over the world quite easily.
Of course, this has created a thriving industry with the screw system engineers trying to stay one step ahead of the ‘Tamperers’. All this could make this next section a bit of a labour of love – it will need constant updating. I’ll see how I get on.
A notable exception is the five pointed Torx, which you have to have security clearance to purchase the driver for. Other than that, really the only way of preventing someone undoing a screw is to use a one-way or headless drive. Of course, you couldn’t undo these either…
NB: I recently saw a ‘Pin-in’ Torx driver for sale in my local hardware store – ‘Nuff said.
Tri-Wing, Triangular Slotted, Tri-groove
Another Phillips product, the Tri-wing is usually used on electronic items to discourage home repair. As the name suggests, it is a screw recess with three radial “wings” and a small triangular hole in the center. A variation in which the three “wings” are joined in the center, with no triangular hole, is known as Triangular slotted.
A similar-looking design in which three short radial slots are not joined in the center is called a Tri-groove screw drive (see the security screws section)
NB: Not to be confused with the ‘Opsit’ Reverse Thread or ‘Left handed Tri-Wing’, which is a sheet metal screw that installs counter-clockwise; so it tightens if you try to remove it.
Triangular recess Security, TP3
Triangular Recess Screws are increasingly being used on electronic consumer goods, such as Game boys. They are also used on fast food promotional toys (go figure)
Tri-Groove, Tampruf, Holt-Head
Tampruf is Australian and refers to both screw heads and nuts.
Rather than the regular bit tips for drivers, these use a socket drive system. This means that they can be fitted mechanically and used where items need to be assembled on a production line, but security is important.
The ‘Holt-Head’ also looks similar to this, but I can’t find any good information on it.
Very similar to the Notched spanner…
Very similar to the Twin Groove. Often seen in Elevators in the USA
Pin spanner, Pig-Nose, Snake eyes
The Pin Spanner is similar to the Twin Groove and Notched spanner.
Tamper resistant screw drives
A Tamper resistant drive is just like a normal drive, but with the addition of a ‘Protruding obstacle’ or Pin somewhere in the socket. The tool then requires a corresponding hole in the driver for the fastener. Usually the hole is in the center, but some are slightly off-center.
I don’t have much to say about these – see the corresponding descriptions for the drives above.
Just like a Torx drive (See above) but with an additional pin.
Pin-In Pentalobular socket Torx Plus
Sales of these screws and drivers are restricted to limit availability.
The One way Clutch screw head features a special ‘Wing Type’ chamfer which provides a drive face for the screwdriver to do the screw up, but causes the screwdriver blade to slip off the head during any attempt to undo the screw.
One-way Pozidrive, ‘Sentinel’
‘”Clutch Head” and “Sentinel” One Way Security Screws provide a permanent fixing yet can be installed using an ordinary screwdriver.
In both Clutch Head (slot wing type) and Sentinel (pozidrive type) formats, the head of the screw has a normal drive face and a chamfered rear face which prevents the screwdriver gaining any purchase when trying to undo the screws.
Once installed therefore these screws will typically have to be drilled out to remove them.’
Download the AutoCAD File
You can download the AutoCAD file for all these Recessed Screw Drives here:
If you download this cad file (and you found it useful) please leave a comment!
You might also enjoy This post on ‘Wood screw head types’
*Yes – I made that one up.
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