Thursday, October 08, 2009

Metric Screws and Pitch

As I was putting together my new bike for its commuter function, I found various useful things left over from my former days as a bicycle commuter, and one of them was a headlight for the handlebars. I needed a headlight, and this one, manufactured by Cat-Eye at one time (but no more) had been a good one. Would it still function?

When I picked it up out of the drawer to which it had found its way over the years, I noticed it was heavy with the batteries that I had negligently left in its case. I anticipated that the batteries would have leaked all over the inside and ruined the headlight. But when I opened the case, the batteries were clean with no leakage. When I tested the batteries, they were dead, of course. But no leakage. Duracells, they were. They must have been in the case for nearly 8 years, sitting in the drawer of a chest in the garage. Yet no leakage. Score a ten for Duracell.

The headlight slides on a mount, and the mount grasps the handle bars. The engineering is ingenious, because you can slide out the headlight and use it as a flashlight, leaving the mount behind on the handlebar. But the mount was missing the screw that fastens it down. The nut was there, sort of embedded on one side of the mount, but there was no screw. It would have been a screw of very small diameter, and about an inch or more long.

I got out the shoebox where I collect all the extra machine screws and nuts that have ever shown up in my life. Actually, a good part of the mass of metal in that box consists of screws and nuts that I inherited from my dad, so there are at least two generations of that hardware. The origins of the box, then, were in my dad's house as he was growing up during the Great Depression. I don't think anyone ever threw away anything during that era that would have even a remote chance of being useful, if not in one's life then in the lives of succeeding generations. Those habits persisted. As I grew up, naturally and with little thought I just knew that it was written that men put extra screws in shoeboxes and Mason jars. So I had this box with machine screws, probably 75 years or more in the making.

None of them seemed to work. The nut that was embedded in the mount would take none of the screws that seemed to be the right size. I looked at the nut in a magnifying glass to see if there was a damaged thread. I couldn't tell, but figured that was it. So I took the screw that seemed right and the nut-that-wouldn't-take to the neighborhood hardware store ("Village Hardware"). I got the old guy there to wait on me and not the kid.

We walked to the back of the store where there is an impressive set of cabinets with all sorts of screws and nuts in little, labeled drawers, wonderfully sorted. (What a great place!) But as we went through the drawers, we could not find a screw to fit. I just knew the nut-that-wouldn't-take was defective, so we looked for a nut like it. But none of the nuts were of the small size of the nut in question, even though the diameter of the hole of the new nuts seemed right. So the new nuts we found wouldn't fit where the "defective" nut had been embedded. But suddenly a light went on in the mind of the old guy (the other old guy), and he said "metric."

Immediately the whole enterprise became political. Here was multi-nationalism, multi-culturalism, One World, free-trade, the UN, probably France, all of that, getting in the way of lighting the street before me as I pedaled up Hammond Drive in the early morning. Metric! The-nut-that-wouldn't-take was metric. I may be a Democrat, but there are limits. This could be one of them.

The reason that the subject nut would not fit on my screw is that metric screws and nuts have pitches that will vary. The US screws in my box seemed just to have one pitch (but maybe not), none of them probably square with any available metric pitch (but I really don't know.) But in metric-land there are different pitches for, I assume, different uses. In addition, the nuts will have a smaller outside diameter, so they will fit in smaller places.

So we walk even further back in the store, and the older (even older) gentleman helping me found a small, flat wooden box, opened the lid, and there were metric screws and nuts. Among the screws was one that fit the subject nut. It had a pitch that fit. The problem was that it was a bolt headed screw, and I needed either a slot or Phillips head, because the screw fits down into a recess that surrounds the head so closely that one cannot get anything around it to tighten. But that problem was solved when I departed Village Hardware and went to the Lowe's in Hialeah, discovering that there is an entire section devoted to metric screws and nuts. I found the slot head screw that I needed.

But at a Hialeah Lowe's you would figure that I would find my metric solution - no one speaks English in Hialeah.

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