Here in the UK, the two most common types of screw are ones with a single, straight cut through the head, and those with a cross cut into the head. They’re commonly known as flat-head, and Phillips. Unfortunately, both these names are wrong. The former is a slotted-head (a flat head refers to the shape of the screw head that can finish flush with the surface, regardless of drive type); while the latter may be Phillips, it’s more likely to be Pozidriv.
Phillips and Pozidriv both have a cross-shaped hole in the head, but it’s important to understand the differences. When using a screw, the biggest problem is camming out. This is where the force on the screw causes the driver to pop out, often damaging the screw or driver in the process. When it happens too many times, the screw can be worn to the point where it’s hard to remove.
There’s speculation that Phillips may have been designed to cam out at a particular force, as this would be useful in assembly as a sort of primitive clutch, to prevent screws from being driven with too much force and stripping the thread. There’s not much evidence that this is true, but it certainly is the case that Phillips screws have a tendency to cam out at much lower forces than other screw heads.
While a Pozidriv screwdriver looks similar to Phillips, the design of the crossed blades in the bit is subtly different, and this means it’s much less likely to cam out (but will if too much force is applied).
You can fit a Pozidriv bit in a Phillips screw and vice versa, but you really shouldn’t. The result will be a cam out at a low force, and therefore a much greater chance of destroying the screw head. Fortunately, it’s easy to tell the difference between the two, as Pozidriv screws should have an additional X marked at 45 degrees to the main drive slots. While Pozidriv allows you to apply more torque than Phillips, if you need more then you might want to consider a hex (aka Allen) or Torx (star-shaped) screw. However, these are more common on bolts than screws.
Picking the perfect screw is a complex question where there’s scope for personal preference, geographic location, and the intricacies of the particular project. However, if you need a rule of thumb: use Pozidriv, unless there’s a good reason not to. Our American friends might not find Pozidriv screws as easily as those of us in Europe, but they’re worth seeking out if possible. Slotted heads have no way of easily keeping the driver central, and Phillips cam out too often. Torx can work well, but the screws aren’t common.
As the screwdriver gets worn by camming out, it becomes more prone to camming out, and so you descend down a slippery slope of stripped screws, jammed joints, and anguish. Getting screws in and out safely starts with the right screwdriver. There are two parts to this. Firstly, you need to make sure you’ve got the correct types and sizes for your screws. Secondly, you need to make sure they’re strong enough to cope with repeated use.
The traditional screwdriver is a single tool for driving one type and size of bit. Alternatively, you can get sets where you can change the bits in a single handle. The former is often easier to work with if you use a limited range of screws, while the latter is often better if you need a wide range of different types. Of course, it comes down to personal preference as well. It’s also common to use driver bits in electric drills, but bear in mind that these can produce significantly more torque than the bits can handle, so make sure you set the clutch before starting, or you’ll damage both bit and screw.
Our Canadian readers might be wondering why we’ve missed out the most popular screw in Canada: the square, or Robertson, head. It’s a great screw design that’s not prone to camming out but, due to a history that’s got more to do with patent law than technical merit, it never caught on elsewhere.
Screwdrivers span a huge range of prices. At the low end, you can get driver sets for just a couple of pounds; however, you can also pay over £100 for a good set. We tested out a Wera Tool-Check Plus set, to see what you can get for £75.49. You get a set of interchangeable bits covering the most common slotted, Phillips, Pozidriv, hex, and Torx bits (and two of some to keep you running when one wears out). The holder spin sleeve allows you to keep the driver steady with your non-turning hand, and also locks in the bits (though we’ve rarely had problems with the bits falling out of the handle).
This isn’t an enormous kit, so if you’re working with a lot of exotic equipment, you might find it lacking. However, we found it complete enough for most screws in our workshop. There’s also a ratchet and socket set, but those aren’t relevant to screws. Perhaps the main thing you pay for is the toughness of the bits. The bits in this kit are made of chrome-moly steel that should keep them going for a long time.
The advantage of a tough screwdriver isn’t that you don’t have to replace it as often (though that is an advantage), it’s that it does less damage to the screws. Worn screwdrivers wear down screw heads, and this means that with a quality screwdriver you’re less likely to end up with stripped screws stuck in things you’re making, and this means fewer headaches.
It can be tempting to buy cheap screwdrivers, but if you’re a maker you’re probably going to be regularly using screwdrivers for some time, and a good set can be a great investment. The Wera Tool-Check Plus is a good option that should last for many years.