Everything you never knew you needed to know about Recessed Screw Drives

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

Tr-Wing Screw Drive 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.

Tri-Slot Screw Drive

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)

Here is a link to the Phillips Tri-Wing Website

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.

Find out more about the ‘Opsit’ system at the Tamperproofwebsite

Triangular recess Security, TP3

Triangle Screw DriveTriangular 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)

You can see an example here at the Security Fasteners web site

Tri-Groove, Tampruf, Holt-Head

Tr-Groove Screw Drive 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.

Here is some good information on the Tampruf system

Twin Groove

Twin-Groove Screw Drive Very similar to the Notched spanner


Notched Spanner

Notched Spanner Screw Drive Very similar to the Twin Groove. Often seen in Elevators in the USA


Pin spanner, Pig-Nose, Snake eyes

Pin Spanner Screw DriveThe 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.

Pin-in Torx

Pin-in Torx Screw Drive Just like a Torx drive (See above) but with an additional pin.


Pin-In Pentalobular socket Torx Plus

Torx Plus Screw Drive

 Sales of these screws and drivers are restricted to limit availability.

Pin-in Square

Pin-in Square Screw Drive



Pin-in Hex

Pin-in Hex Screw Drive



Pin-in Phillips

Pin-in Phillips Screw Drive



One-Way, Clutch

One-way Screw Drive

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’

One-Way Pozi Screw Drive

‘”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.’

Find out more about One Way Drives at the Insight Security Web Site


Download the AutoCAD File

You can download the AutoCAD file for all these Recessed Screw Drives here:

[Download not found]

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’


Wikipedia – A List Of Recessed Screw Drives

Instructables – When is a Phillips not a Phillips

DiyFaq Wiki – Screws

Sizes.com -Screw drives

Wapedia Mobi – List of screw drives

Schools Wikipedia.org – Screw

Fastener dimensions – Bolts screw heads

*Yes – I made that one up.

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