12-24 is presently more normal than 10-32 in pre-strung racks. 12-24 clasp are somewhat bigger than 10-32 and have courser strings. The term 12-24 comes from Unified and American Screw Threads for Bolts, Nuts, and Machine Screws principles distributed by ANSI B1.1-1974. The number "12" is just a size designator with no mathematical significance. The number "24" alludes to 24 strings for every inch. You can distinguish a 12-24 screw by estimating the width with a ruler at somewhat under 7/32″ (marginally bigger than 3/16″ or 0.210″).
