BTW, how big are #6, #8 and #10 machine screws again?
A while back, I posted a homemade chart showing decimal equivs for machine screws and small metric fasteners. Probably lost by now, though. Machine screws follow an archaic system that makes sense if you follow the system. It does not fit into our modern measurement system, and is often duplicated by fractional sizes.
Almost, within a couple of thou anyway.
Machine screws have a base size of 0.060 in. Why? I don't know, but that's the system. For each size, add 0.013 in. A 1-64 machine screw is 0.060 plus (1x)0.013 = 0.073 in dia. A 2-56 = .068 + (2x.013) .026 = 0.086. Again, why .013? There are thread sizes at 8 TPI intervals, again, why? Who knows, the system is lost in antiquity. Maybe a very old copy of Machinist's Handbook could shed some light. But me, I don't care unless I run into one, a rarity these days.
And so on up the chart... A 6-32 screw is 0.060+(6x.013)=.138 Convienetly, a Nr 5 screw is 0.125 in, 1/8th. A Nr 8 is .060 +(8x.013) = 0.164 in. A Nr 10 is at 0.190, with a 3/16" at .1875. Most hardware stores use one and call it the other. Maybe that has some bearing on the [why] of 0.013. 1/4 in vs Nr 14 is just a few thou different.
The old school system goes far above 1/4 in, almost to 3/8 in. Modern sizing has taken over most sizes above 1/4 in, with Nr 12s being still in use but rare. There are(were) other sizes of fractional, as well. I recently acquired taps for 1/16-80. At 0.0625 vs 0.060, they will
almost work interchangably. Almost ... ...
I personally work with tiny sizes, less than Nr 0. Nr 00 or 2/0 steps down the same way, at -.013=0.047 in. There are several sizes smaller, optical screws and the like. 3/0 is the smallest size I work with, but there are several smaller. Then there's metric, re: modern eye glasses. If you pursue it much further, all I can do is wish you luck.
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