Despite years of working with tiny hardware, the inevitable decay of age has made it difficult to distinguish the smaller numbered screws by sight or touch.
The typical thread gauge doesn't include the smaller sizes so I decided to make myself a dedicated small screw thread gauge. A scrap of bronze (?) 1-3/8 x 1/2 x 1/8 was selected for its friendly threading behavior. (If you make one of these, by all means avoid steel, especially stainless; also aluminum for its gumminess.)
From left to right the screws are 00-90, 0-80, 1-72, 2-56, 3-48, 4-40, 5-40. For scale, the giant 5-40 is 0.125" diameter and the 00-90 is 0.047". I didn't include the even smaller 000-120 and 0000-160 since I seldom use them and the screws bend too easily on something that's going to be handled like this will.