Square Drive Screws
March 6th, 2006
Flathead screws are a pain because it’s easy for the screwdriver tip to slip out of the slot. They’re really unsuited for power driving.
Phillips head screws are a pain because the screwdriver tip will cam out under high torque use. I’ve read that phillips screws were actually designed for automated assembly applications, because the design made it easy for an automatic screwdriver to find purchase, screw and then release. That is to say, cam in/cam out is a designed-in feature.
Robertson, or square drive screws, on the other hand, are designed to keep a tight hold on the screwdriver tip under both low and high torque applications. They’re used most commonly in Canada, where the Robertson drive screw was actually invented. They’re not as common in the US.
As the name implies, the screw has a square hole in it, into which a square bit is inserted. The bit is slightly tapered, so as you insert the bit, it holds securely to the screw, so you can actually put a screw onto the screwdriver and then drive it overhead, one handed, and the screw won’t fall off the screwdriver. Nice.
Cam-out is extremely unlikely. You can get some serious torque on these screws without the danger of the tool slipping.
You can find a wide variety of square drive screws and the screwdrivers to drive them at McFeely’s. You can also find a pretty decent explanation of the benefits of square drive screws here.