If you’ve ever had the pleasure of assembling low-cost furniture yourself, you know it can be frustrating. Indecipherable directions and missing screws can add hours or even days to what should be a simple build. The fasteners are always of the lowest quality and it’s a wonder that the particle board will hold them at all.
There is a less obvious pitfall when assembling your own furniture, however, and it’s one that is often overlooked. The manufacturer knows about it, but will never warn you. It’s easily remedied and will save your wrists, your screw drivers, and your patience from being worn out.
I discovered this pitfall when assembling bookcases from a certain Scandinavian discount furniture chain that has not yet graced Iowa with its presence. As I drove in the screws I found that they got really hard to turn towards the end. At first I thought it would just take a bit more elbow grease, but then I noticed the screw driver wasn’t really seating correctly in the screw. Something was wrong, and it wasn’t a matter of muscle. So I took a real close look at the screw and there they were: four thin lines on the screw head that told me this isn’t a phillips-head screw.
In the U.S., the phillips drive and the flat head have always dominated, so much so that many people own no other drivers. The Canadians are fond of the Robertson drive, and electronics manufacturers prefer torx, but you’re unlikely to mistake one of those for a phillips or have much luck turning them without the proper driver. The screw I had encountered, which seems to be popular in self-assembly furniture, is a Pozidriv and it’s a bit sneaky. It looks to the untrained eye like a phillips, and you’ll have some luck turning it with a phillips driver, but to put sufficient torque on the screw you’ll need a Pozidriv driver to match.
The difference between the two drivers is in the blades. A phillips driver will have blades that have a taper, like a wedge. If you put too much torque on the driver it will slip out of the screw head, or “cam out.” A Pozidriv driver, on the other hand, has rectangular blades with perfectly parallel sides. This allows the user to put more torque on the screw without the driver being pushed out of the screw head. A second feature of Pozidriv drivers are four additional ribs, or splines, in between the blades of the driver. Seeing those is a dead giveaway that you’re looking at a Pozidriv driver.
So now you know the one sneaky pitfall that can make furniture a pain to put together. You’ll probably start to notice Pozidriv screws in more places and will be able to correct your friends’ choice of drivers when you see them using the wrong one. (They’ll appreciate that.) Now if you can eye the difference between a triple-square and a double-hex, you’ll be a real screw drive connoisseur.
Paul Henley
Fab Lab Member