Screwed Again

by Fred DeSantis

Just when you think you know something about fasteners, your little British car tells you that you really don’t.

All I wanted to do was adjust the doors! The door hinges on my 1967 Austin-Healey 3000 are fastened to the body with 8 screws, 4 to a hinge. The driver’s side had the original screws still in place. The bad news was that most of them were rounded out and my Phillips screwdriver just would not work. A few even had the remains of drill bits that had broken off inside the head while someone was trying to drill them out. After some work, I was able to remove one. The screw looked like a common Phillips head but slightly different. With a bit of research, I was able to identify the screw. It was not a Phillips at all but a Posidriv, which looks like a 4 slot Phillips but with another set of 4 radial slots machined in.

Phillips—4 slots. Pozidriv—8 slots. But why?

Phillips head screws were patented in 1935 by Henry Phillips as an improvement over the single-slotted screw. The 4 slots keep the driver centered. A great improvement over a single slot screw, but the Phillips was still very prone to slippage, the fancy term being “cam out”. When the patent ran out for the Phillips head, the Phillips Screw Company improved the design and came up with the Pozidriv—pronounced “Poz-i-drive.” Having the 8 radial slots greatly increases the bite of the driver, reduces stripping and cam out, and allows for more torque without damage.

So whoever tried to remove the Pozidriv screws in the Healey’s hinges probably used a regular Phillips head driver, thus negating the strengths of the Pozidriv screws, and accidentally rounded them out. Pozidriv screws require a Pozidriv driver; you can fit a Philips driver into a Pozidriv screw, but you risk damage. I was able to purchase the correct Pozidriv socket driver and easily remove the screws that were not totally damaged. Of course, the damaged heads had to be drilled out and removed with an extractor. I had to remove that door! New correct Pozidriv screws, Moss 323-235, were ordered and installed with a touch of Never-Seez, and now all is well.

Where will you find a Pozidriv screw in your car? I have read that they do lurk unexpectedly in all British cars.