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

Paul Munford

14 years ago

This started as a simple idea to start creating more blocks for download. Unfortunately once I realised how many screw drives there were available, my obsessive compulsive side kicked in and I had to document them all! If you see any you think I’ve missed, please let me know ;-)

Screw heads come in a range of sizes. A screw ‘Drive’ is the system used to turn a screw. The drive is a feature on the screw that allows it to be turned. The ‘Driver’ is a mating tool, which is used to turn the screw

Robertson Screw Ad

A little bit of Screw history

The idea of the screw was first explored by the Greek mathematician Archyta. Wooden screws were used in early machinery such as wine presses.

The first documented use of a metal machine screw was by a German clock maker in 1513. The head was made by flattening one end of a wire and the threads and slot were hand cut with a file.

Screws weren’t machine made until Henry Maudslay, a British engineer, Invented the Screw lathe in 1797. Another British Engineer, Jesse Ramsden continued to develop the screw Lathe to make mass Production possible.

Screws with tapered points (‘Gimlet’ Points) weren’t mass manufactured until George Nettlefield started making them in the 1840s

Common Wood Screw Recessed Drives

Every woodworker should have a set of Bits in his kit for these drives.

Slotted, Flat, Straight

The traditional wood screw has a single slot in the fastener head and is driven by a flat-bladed screwdriver. Driving by hand or using a ‘Yankee’ pump action driver is recommended due to the tendency of a power driver to slip out of the head and damage the surrounding material.

Frearson, Cross Head, BS ‘Type H’ , ANSI ‘Type II’, Reed & Prince, (R&P)

The Frearson screw drive was developed by an English inventor named John Frearson in the 1870’s . It was produced from the late 1930s to the mid-1970s by the former Reed & Prince Manufacturing Company of Worcester, Massachusetts.

The Frearson pre-dates the Phillips and has a more pointed 75° V shaped recess. The tool recess is a perfect cross and allows mechanical driving without ‘Cam-ing Out’ (slipping). In theory one driver or bit fits all screw sizes, although different sizes are recommended.

Phillips

The ‘Phillips’ Head was invented by John P Thompson, who sold his self-centring design to Henry F Phillips after failing to interest other manufacturers. Henry Phillips is credited with developing the idea to the point that it was adopted by major manufacturers, such as General Motors.

Unlike the Frearson, The self centring Phillips is Designed to ‘Cam-Out’ when the driver reaches maximum torque. This saves the screw from being over tightened or the head from being damaged or broken off.

This might be frustrating on the bench, but it was a design feature when used on the production line. It is important not to mix up Phillips Heads with ‘Pozidriv’ Heads because the drivers are not compatible and you can damage the screw head.

Find out more about Phillips head drives from the Phillips web site.

Pozidriv (PZ), Pozidrive, BS ‘Type Z’, ANSI Type 1A

The Pozidriv Recess was also designed by the Phillips company, and is designed not to Cam-Out. The distinctive ‘Cross’ mark is used to distinguish between the two. The Pozidrive system is compatible with the Supadriv system.

Find out more about the Pozidrive system on the Phillips web site.

Next – Less common recessed 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.

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…

Combination drives (Combo-head, Combi-head)

You will find these on Kitchen fittings and knock-down fasteners. The combination reccessed drive heads mean that you can use what ever driver you have handy…

Double slot

Not strictly speaking a combination drive, this head has two slots so you can pick the most convenient one to stick your driver in. Usually seen on roofing bolts.

Combination Phillips-Robertson, Quadrex, Recex

Combines the Best Features of Cross recess and square socket drives. The Quadrex recess increases productivity by incorporating the torque transmission and cling fit of the Square Socket drive with the desirable field repair and retrofitting features of the Phillips drive.

Here is a good visual of the Quadrex drive

Robertson also have a version, know as the Recex drive system.

Square-Drive, PoziSquare-Driv

Phillips have their own brand Square-Driv and PoziSquare-Driv combination drive systems.

Combination Phillips-Slot, Cross-Slot

Apparently popular in the electrical field. Also used on concealed (European Style) Cabinet hinges.

Combination Slot-Robertson, Slot-Square

I have no further comment…

They is what they is…

Combination Hex-slot

Combination Torx-Slot

Combination Hex-Slotted

Combination Hex-Phillips

Qua-Drive, Combination hex, slotted, Phillips, square

The Qua-Drive is from Avanti screws

Tri-Drive, Slotted, Philips, Square

The Tri-Drive is another product from Avanti

Next – Security 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

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)

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

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)

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

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.

Here is some good information on the Tampruf system

Twin Groove

Very similar to the Notched spanner…

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.

Pin-in Torx

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.

Pin-in Square

Pin-in Hex

Pin-in Phillips

One-Way, Clutch

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.’

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