Today’s topic is drive mechanisms for fasteners. We’re going to break this into two sections: regular drives and security drives. Primarily, we’re discussing indented screw drives which means the drive mechanism is punched or cut into the screw. (Many bolts and some screws may have external drive mechanisms such as a hex head and we’ll mention those later in this post.)
A good source can provide you with a lot more than just slotted and/or Philips. And a good source can explain the differences and why they may be appropriate for your particular application. No matter what advice we give, the most common reason a customer picks a particular drive? “I want it to match all the other screws.” This is why electrical plates are still commonly installed with oval/flat slotted screws instead of Philips. It’s also a bad reason, because using a slotted screwdriver (which notoriously slip out of the drive) around electricity is dangerous. In my home, I replaced all the slotted screws in electrical socket covers with Phillips.
Now that you have some things to think about, let’s talk about the six most common screw drives. Of course, this is not a complete list but is mean to give you a brief overview. There are many more drive styles not listed here. This is a discussion of some of them, or at least the ones you’re likely to run into.
If you have questions about the differences and benefits of each kind in a given application, ask us! You can combine many of these together to make various forms of combo drives. You can add pins to many of them to make security screws. Often the differences between some of the polygonal drives is hard to tell apart with the naked eye.
The History of Some of Common (Indented) Screw Drives
(The numbers correspond to the numbers in the picture I made to the right)
- The slotted drive has been around since at least the 1600s (renaissance-era!) and was the drive on some of the very first threaded screws. The slotted drive was designed to enhance rotational leverage and simplified the installation of for fasteners. Oddly, they remain popular to this day for reasons I fail to understand when much better choices exist. No patent or trademarks apply.
- In 1908 the Robertson® Drive (commonly called square) came along shortly after its inventor, Canadian P.L. Robertson, injured himself when his slotted screwdriver slipped from the head of a screw. The primary goal of Robertson’s drive was to prevent slippage, which remains a common, constant complaint with slotted drives. When the Robertson Drive was first introduced, torque limitation on tools was non-existent, meaning that the Robertson drive had the potential to cause significant damage to both tooling and fasteners by over-tightening. By 1918, the NYC Water Department had come up with the first toque-limiting tool though the first patent wasn’t filed until 1931, by John H. Sharp of Chicago. The name Robertson® is trademarked (and capitalized because it’s an eponymous name) and you should always use the generic “square” drive unless you are providing Robertson® brand fasteners. No patent applies.
- The Hexagon (or Allen) Drive came about at the turn of the century and was ultimately patented by W.G. Allen in 1910; it didn’t become particularly common until the 1930s. As with the Robertson drive, hexagon drives had the potential to engage a little too well with a fastener and could cause damage through over-tightening. This drive mechanism is typically only seen in socket-style products. It is common to call these Allen drive, but most in the industry avoid that eponym. There is no patent or trademark in effect on this drive.
- The Phillips Drive is arguably the most well-known drive type there is and dropped into the world in 1935 courtesy of John P. Thompson. The Phillips drive features a much shallower socket than square or hexagon drives, which allowed the driver to disengage under excessive force. The Phillips drive is sometimes criticized for its tendency to cam-out at relatively low torque levels which can cause slipping or rounding of the screw drive. The patent and trademark on the original Phillips drive have expired, but because it’s a proper noun it remains capitalized. The Phillips Screw Company still exists. There is an even newer patented version of the bit called the ACR® Phillips which has little ribs on the bit, and these are fantastic and reduce cam-out; in fact, the ACR® stands for Anti Cam-out Ribs! Sadly, they aren’t very common but we’re happy to provide them to our more discerning customers.
- The Pozidriv® (it has no E at the end of the name and is commonly misspelled) arrived in 1955, a full 20 years after the Phillips, as an improvement. It features a blunt tip, and four radial grooves for increased driver engagement. They are, visually, very similar to Phillips drives, but can be easily distinguished by the four shallow radial markings on their heads. Pozidriv® is a registered trademark of the Phillips Screw Company, though I could find no record of a valid patent. This system is much better than the original Phillips and is wildly popular in Europe; why it hasn’t caught on here in USA is a mystery to me.
- The Torx® Drive (generically called star-drive or 6-lobe) came along in 1967 courtesy of Camcar. and was designed to improve upon the torque transmission capabilities of earlier drive designs. The hexalobular design of the Torx® socket is an improvement upon the hexagon drive (see #3) due to the addition of six deep lobes, which allow force to be transmitted at close to a 90-degree angle in each corner, and greatly improves its ability to transmit rotational forces. The hexalobular design is also stronger and more resistant to rounding than a hexagon drive. By the time the Torx® drive was introduced in, torque limiting features were already common in drills and tooling, reducing the pitfalls of previous socket designs. Interestingly, when the Torx® drive was first introduced, it was considered tamperproof by many due to its unique shape, but it became so popular, and its availability and use so widespread, that its tamper-resistant properties quickly vanished. The name is trademarked, and if you order a screw be sure to specify 6-Lobe because if it’s called Torx® you will pay more for licensing. (It’s just like Coke. If you ask for Coke, legally the supplier has to give you a Coke and not a Pepsi. Or they can ask if you prefer Pepsi. But if your supplier has both – and on some fasteners we do – we’ll give you what you ask for.)
And that is your quick introduction to the six most common internal fastener drives. Many people will never need anything else!
Sampling of The Many Types of Screw Drives (Including Tamperproof)
Since there is no official definition of what does and doesn’t constitute a security drive, I get to decide for the purposes this article 😊 While items with an asterisk (*) are considered to be security drives, not all of them are very secure. Just because something is considered a security screw, doesn’t mean it’s a very good one. 6-Lobe/Torx® drives are no longer considered security drives because you can get the drivers/bits everywhere, even at your local dollar store. Items marked with a ‡ are better choices for a security screw because it’s harder to defeat the security mechanism. One-way screws are not recommended in most instances because they cannot be removed reliably without damaging the product they are installed into.
I spent a week making these charts, so I hope my readers are suitably impressed by my complete (lack of) artistic talent.
INTERNAL DRIVE: Slots and Cruciform (Cross) Drives
Discussion of above group: Quadrex® is sometimes known as Recex® which is another brand name. Frearson (also known as Reed & Prince®), JIS-B-1012, and French Recess, all look similar to Phillips but aren’t quite the same (French Recess is a cross-slot that doesn’t go all the way through). Get a magnifying glass and look and you can spot the differences.
Personally, I like Quadrex® the best of the above lot, so I don’t have to worry about what bit I might have laying about. But there’s limited availability and a cost penalty (except in Particle Board Screws where it’s standard.) I don’t like all the “odd” drives for standard use because there’s always a bit problem and those bits are often not available in longer lengths. For Phillips I much prefer the ACR® bits. Though screw-wise I aim for Pozidriv® when available. Everything with fasteners is a trade-off.
INTERNAL DRIVE: Hexalobular Drives
Discussion of above group: Torx® is my favorite standard drive style of all of them. It doesn’t slip, I get good bit engagement, and proper driving torque. But it simply isn’t widely available and there is a significant cost penalty when buying Torx® fasteners. Some of these obscure bits are only available as made to order (MTO). Let me share a dirty little secret with you on some of these “security” drives: they don’t keep crooks at bay. For many of these bits, it’s possible to get a smaller slotted screwdriver, and wedge the blade between the points (like a Mortorq® or Tri-Wing®); while it ruins the screwdriver, you almost always get enough engagement to start to back the screw out. After that it’s all over for any security you thought you had. No matter what drive you want, we at Hardware Everywhere are happy to supply it to you in any configuration and material.
INTERNAL DRIVE: Polygonal Drives
Discussion of above group: The first two in the first column are common and used widely. The others are far less available. From a security standpoint, the pin-in items are better than ones without a pin because they prevent the slotted screwdriver trick that I mentioned previously. Unfortunately, those socket pin-in screws of which everyone has become fond of have bits that are now available through many online resellers reducing their value as a security bit considerably.
INTERNAL DRIVE: All Other Drives
Discussion of above group: The best of this group, by far, is the Microtech 3-Pin® design. Sadly, I’ve never actually seen one available for sale off-the-shelf. What is commonly available, and we at Hardware Everywhere are fond of them, are the Spanner drive screws (the term Snake-Eyes® is great but it’s a particular brand.) One thing to be careful of with Spanner Drives, you have to buy your screws and bits from the same vendor at the same time because there are two standards for hole spacing and they are off by about 1/32nd of an inch on a few sizes making them non-interchangeable. Spanners have a cost penalty because each screw has to be precision drilled.
Discussion of The Many Types of External Drives
When you put in a hex bolt with a wrench, that’s an external drive. Hex and square are the most common external drives. There are also spline drives (12 point) and penta-drives (5 sided). None of these are security drives per se, but rather designed for specific applications. For example, stainless steel Penta bolts are very popular with nuclear reactors on certain critical assemblies. Why? It’s a visual aide to keep a worker from accidentally opening the wrong hatch and releasing fatal radiation. Death is an awesome motivator for innovation!
Some bolts have round heads and no drive (carriage, step, timber, plow, elevator, etc.). Why? They have necks that sit in cut-out slots/grooves and they are controlled by the tightening of the nut.