It doesn't matter if your problems involve determining the "small end of a reamer" or the "thickness of a Woodruf key size" the Simple-Fyer is the answer. Body Drill? Basic OD of a screw? Threads per inch or fine versus coarse? A cardboard disc with multiple circles, any Christmas problem involving sines, cosines, tangents, cotangents, secants or even CO-secants are no problem with the Simple-Fyer. This year, save time with Derck's. Only one dollar at all Cardboard Gauge Dial stores!
Derck's Gauge Dial, 1943. Collection Jim Linderman