Monday, July 30, 2012

When to give it up

Recently, I've been discussing fasteners. Screws, bolts, Allen keys and such. There are many types of fastener, and many methods of driving screws. The most common one, in the US at least, is the venerable Philips drive; the cross-shaped slot that generally ends up burred and worn to uselessness within three drivings. Its dominance is a historical accident; it was adopted by Ford because it was available with reasonable license fees, and because it's designed to "cam out". It's very difficult to overtighten a Philips-head screw, because the tool will slip out at high torque. This meant Ford could use cheaper tools. Of course, there's a downside to the cam-out; it's easy to strip a Philips-head screw, and because it's harder to unscrew than to tighten, a securely-tightened screw will be nigh-impossible to remove. These are major reasons why Philips-head is these days largely confined to small electronics work and wood screws.

Speaking of wood screws, the major type of head in Canada is the Robertson. Robertson was offered to Ford, but it had some disadvantages; first, they wanted more money to license it, and second, it doesn't cam out. The square bit stays in the screw, and the whole setup binds. This makes it ideal for hand tools, as does the ability to securely set the screw on the bit prior to driving (anyone who's tried that with non-magnetic Philips screws will know what a boon it is to be able to put the screw on the end of the driver), but powered tools need a torque-limiting device to avoid breaking things.

Car manufacturers have never liked normal people messing with their cars, and once torque limitation had become cheap, it was inevitable that the fragile, unreliable Philips head would give way to something else. The chosen successor was Torx, a sort of six-pointed star; other than the form of the recess, it's similar to Robertson in its advantages and disadvantages. So why go with Torx, rather than Robertson? The main reason was to keep us from working on cars. Torx bits, when it was new, were a pain to get hold of, whereas anyone who can get to a hardware store could get a Robertson bit; just because it was mostly popular in Canada doesn't mean it was unkown in the US. Nowadays, Torx bits are cheap and easy to get hold of; I have at least three sets knocking around, and at least a couple of the anti-tamper ones with the hole in the middle of the bit.

So now, wood screws have Robertson, and car parts have Torx, and all the niches for Philips have a better competitor in them. Why does Philips keep knocking on?

Because it has a massive user base. Everyone, and I mean everyone, owns a Philips-head screwdriver or five. The car nuts have their Torx bits, but they always come with Philips bits as well. The people who care about woodscrews have Robertson bits, but frankly such people are a fringe group in the US. The vast majority of people buying woodscrews will buy Philips-head, because they already own the bits to drive them.

Personally, I've decided that if at all possible I'll go for Robertson woodscrews. My screwdriver collection includes all three sizes of that bit (as compared to the range from 000 to 4 needed to cover the spectrum of Philips, or the T1-Tn of Torx; although above T10 it tends to go by fives) and so I get the benefits of easy location and secure torque transfer without need for axial pressure essentially free. I may be an American these days, but I can at least admit that Canada does some things right.

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