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

Less Common Wood Screw Recessed Drives

These drives work just great, but don’t forget to check you have the appropriate bit when you buy the screws!

Supadriv, Supadrive

The Supadrive is a continued development of the Pozidriv. The screw head is similar to Pozidriv but has only two identification ticks and the secondary blades are larger. It is superior to the Pozidrive, but completely compatible.

Phillips II

The Phillips II Has mating serrations between Recess and driver to grip the screw more securely. The serration system is know as the ‘ACR’ system, or ‘Anti Cam Out’.

Find out about Phillips II and the ACR System on the Phillips website

Phillips II Plus

The Phillips II Plus system was developed  to avoid head stripping. The Phillips II Plus system has ribs on the driver bit that seat on a ledge within the recess that makes screw driving easier and creates a ‘Stick fit’. The Phillips II Plus has it’s own driver but can also be driven by a Standard Phillips or square (Robertson)  Driver.

The Phillips II System has it’s own web site

Square Socket, Robertson

An early square drive wood screw US patent was issued to Allan Cummings on March 30, 1875, but credit is given to the Canadian P.L. Robertson who  invented the ‘Robertson’ screw and screwdriver in 1908 and received a patent in 1909.

Robertson refused to allow anyone to make the screws under license. Henry Ford tried out the Robertson screws but when Robertson refused to license the screws to Ford, Ford realized that the supply of screws would not be guaranteed and chose to only use them in his Canadian cars. Robertson’s initial refusal to license his screws prevented their worldwide adoption.

The Robertson Recessed screw drive web site

Other Recessed Screw Drives

These drives are more likely to be found on set screws, machine screws or Bolts than Wood screws.

Hex Socket, Hex key, Allen Key, Unbrako, Inbus-key

The first recorded development of an internal-wrenching hexagon drive is that of the Standard Pressed Steel Company (SPS) of Philadelphia USA in 1911.

SPS gave their line of screws the ‘Unbrako’ trade name. It seems that they wanted to produce their own fasteners in House and created something that wouldn’t infringe on the Square ‘Robertson’ Socket patent.

The design was ‘reinvented’ all over Europe and became established during the second world war.

Read about the Hex Socket drive on Wikipedia

Pentalobular Socket

The Pentalobe screw drive is a five-pointed  system being implemented by Apple in its products It resembles a Torx and does not currently have an off the shelf driver available (It therefore falls into the ‘Obscurity is Security’ category) .

Pentalobe screws were first used by Apple in mid-2009, holding the battery in the MacBook Pro; smaller versions are controversially now used on the iPhone 4and the MacBook Air.

Read more about Apple’s plans to ‘Secure’ your iPhone

Hexalobular socket, Torx, Star Head

The ‘Torx’ Head was Invented by General Motors in the 1960’s. Like the Pozidriv the motivation was to come up with a better screw drive for mechanical screw insertion on the production line. This meant no Cam-Out, and no damage to the head or driver. An alternative brand called the ‘TTAP’ is also available

Check out the TTAP Drive Website

Uni-Drive, Uniscrew, Securiscrew

I’ve found a lot of marketing information about this new type of drive, but very little else. I’ve included it  just because it’s so new and exciting! Either we will all be using them by this time next year, or this will be the last you ever heard of them…

The Pentagon type is rumoured to be an ‘Anti-Tamper’ variant. an even more complex ‘Offset rotation’ pentagon could become available.

F ind out about Uni Drive screws in this Article on The ‘Engineer’ web site

Double Square, Scrulox

Rumoured to be another Robertson Invention. An 8-sided (Double Square) decorative design that can be used with a standard Robertson bit, or for additional torque, a ‘Scrulox’ bit.

These double square fasteners are used on Haulmark trailers and other industrial designs, but I can’t find any reference to them on the Robertson site…

Lox Driver

This is another new kid on the block that I’ve never seen in real life. The Lox system has 12 points of contact, stick fit and can deliver high torque even off angle.

You can find out more about The Lox System here

Mortorq

Another one from the Phillips stable, developed for the Aerospace industry. Reputed to be lighter than corresponding fasteners.

‘Mortorq’s patented drive system provides full driver contact over the entire recess wing,resulting in extremely high torque capability without risk of damage to the screw head or surrounding areas.’

Check out the Phillip’s Mortoq Website

Torq-Set, Offset Cruciform

No prizes for guessing that this is designed by Phillips, the Torq-set is one more product aimed the Aerospace market. Also available in an ACR (Anti-Cam-out) Flavour.

Find out about the Torq- set on the Phillips Web site

Double Hex, Double Allen, Bi-Hex, 12 point socket

Just as it sounds, double hex drives have a socket shaped as two overlapping rotated hexes. It looks similar to triple square and spline screw drives, but they are incompatible; However standard hex keys can be used with these sockets.

This design doesn’t make a great driver socket as it is almost circular and therefore likely to become stripped. You are more likely to recognised this design from your socket set. In this case the driver (socket) has the double hex recess and it is designed to turn Hex Bolts.

Triple Square, XZN

A Triple square screw drive has 12 equally spaced tips, each with a 90 degree angle. Its name derives from overlaying 3 equal squares to form the pattern. Triple square drives are used in high torque applications, such as cylinder head bolts and drive train components. Triple square fasteners are commonly found on German cars.

12 Point Torx

Again, you are more likely to see this as an externally driven fastener with a recessed socket drive.

Bristol, Fluted

The Bristol screw drive is a spline shaped with four or six splines.

One of the main advantages to this drive system is that almost all of the turning force is applied at right angles to the fastener axis, which reduces the possibility of stripping the fastener. For this reason Bristol screw drives are often used in softer, non-ferrous metals.

Find out more at the Bristol wrench website

Polydrive

The Polydrive screw drive is spline shaped with rounded ends in the fastener head. The tool has six flat-tip teeth at equal spacing; the sizes are determined by the diameter of the star points.

Its primary advantage is over older cam-out-prone screw drives, because it resists cam-ing out. It is used primarily in the automotive industry in high-torque applications, such as brakes and drive shafts.

Find out how the Polydrive works at the Brugola site.

Bat-Screw

Seen in detective comics #41, in which Batman and Robin briefly take some time off crime fighting to catch up with a few jobs around the house.*

You might find out more here

Clutch, Types A & G

There are two types of Clutch screw drives: type A and type G.

Type A, also known as a standard clutch, resembles a bow tie.These were common in GM automobiles, trucks and buses of the 1940s and 1950s.

Type G resembles a butterfly. This type of screw head is commonly used in the manufacture of mobile homes and recreational vehicles.

NB: One way drive systems are also know as ‘Clutch drives’. See the entry under Security screws below.
Next – Combination drives…