If you make miniatures you certainly don't have to use a lot of material making a thread checker plate. This one...

is 1.25" long and covers most of the sizes encountered in my model making. From the left, the threads are:

5-40, 4-40, 3-48, 2-56, 1-72, 0-80, 00-90. The screw lying on the (0.75" diameter nickel) is a 00-90. Missing are the 000-120 and 0000-160, both of which are watchmaker size. I try to avoid them.

For the benefit of the folks unfamiliar with the nomenclature idiocy of the inferial system, the diameter formula,

OD = 0.013*N + 0.060

for numbered screws can still be used form screws smaller than N=0. "Simply" count the number of leading zeros, subtract one and apply a minus sign. This leads to:

00 => N = -1

000 => N = -2

0000 => N = -3

so a 0000-160 screw has a nominal diameter of 0.060 - 3*0.013 = 0.021" or about half a mm.

This is why you should never construct a nomenclature system that's terminated at either end unless that termination represents a physical limit. Naming things by size is permissible because nothing can have a negative size. Arbitrarily setting the zero at 0.06 or labeling drills with letters of the alphabet will lead to confusions like the 0000 debacle.

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