TapSizes Tap Sizes have been standardized to conform with those of standard screws, bolts, and studs. 18 16 14 13 12 11-1/2 11 10 9 8 7 6 5-1/2 5 4-1/2 4 3-1/2 3-1/4 3: 0.012500 0.013888 0.015625 0.016666 0.017857 0.020000 Formula for Obtaining Tap Drill Sizes (Select nearest commercial stock drill) FastServiceTaps; MSDS Download; Tap-Drill Size Calculator; THREADPRO ; LITERATURE. Catalogs; Brochures; Literature Request; OSG Shape It 5/16-18 UNC H3 2FX 2.5P HY-PRO AL STI 1303900900: 5/16-24 UNF H3 2FX 2.5P HY-PRO AL STI: 133: 1303900908: 5/16-24 UNF H3 2FX 2.5P HY-PRO AL STI V: 19: 1303901000: 3/8-16 v6Xp.