B.A. thread / American thread specification substitution table Here's a chart collected by Alan Frisbie: Here is my table of British, American, and Metric machine screws and their tap drills. This has been gleaned from a variety of sources, none of which are guaranteed to be perfectly accurate. In particular, there is considerable debate over the "correct" tap drill to use, hence some alternates are offered. This list is sorted by outside diameter for convenience in selecting the nearest size in another series. I would appreciate any corrections, additions, comments, etc. British American Metric Outside Tap Tap Drill Alternate Alternate Sizes Sizes Sizes Diameter Drill Diameter Tap Drill Tap Diam. (inches) (inches) (inches) ======= ======== ======= ======== ===== ======== ========= ========== 16-BA .0311 0.60 mm .0236 15-BA .0354 0.70 mm .0276 14-BA .0394 0.80 mm .0315 13-BA .0472 0.98 mm .0386 12-BA .0512 1.05 mm .0413 0-80 .0600 3/64 .0469 1/16-60 .0625 3/64 .0469 11-BA .0591 1.20 mm .0472 10-BA .0669 #54 .0550 1-64 .0730 #53 .0595 1-72 .0730 #53 .0595 9-BA .0748 #53 .0559 2-56 .0860 #50 .0700 2-64 .0860 #50 .0700 8-BA .0865 1.8 mm .0709 #50 .0700 3/32-48 .0937 #48 .0760 7-BA .0983 #47 .0785 3-48 .0990 #47 .0785 3-56 .0990 #46 .0810 #45 .0820 6-BA .1102 2.3 mm .0905 #43 .0890 4-40 .1120 #43 .0890 #44 .0860 4-48 .1120 #42 .0935 #43 .0890 3.0-0.6 .1181 2.4 mm .0945 3/32 .0938 3.0-0.5 .1181 2.5 mm .0984 #40 .0980 1/8-40 5-40 .1250 #38 .1015 5-44 .1250 #37 .1040 5-BA .1259 #37 .1040 3.5-0.6 .1378 2.9 mm .1142 #33 .1130 6-32 .1380 #36 .1065 6-40 .1380 #33 .1130 4-BA .1417 3.0 mm .1181 #32 .1160 4.0-0.75 .1575 3.2 mm .1260 1/8 .1250 4.0-0.7 .1575 3.3 mm .1299 #30 .1285 3-BA .1614 #29 .1360 8-32 .1640 #29 .1360 8-36 .1640 #29 .1360 2-BA .1850 4.0 mm .1575 #22 .1570 3/16-24 .1875 #27 .1440 3/16-32 .1875 #23 .1540 10-24 .1900 #25 .1495 #26 .1470 10-32 .1900 #21 .1590 5-0.9 .1968 4.1 mm .1614 #20 .1610 5-0.8 .1968 4.2 mm .1654 #19 .1660 1-BA .2086 4.5 mm .1772 #16 .1770 12-24 .2160 #16 .1770 12-28 .2160 #15 .1800 #14 .1820 7/32-24 .2187 #16 .1770 7/32-26 .2187 #15 .1800 7/32-28 .2187 #14 .1820 0-BA .2362 5.1 mm .2008 #7 .2010 6-1.0 .2362 5.0 mm .1968 #9 .1960 1/4-20 .2500 #9 .1960 1/4-20 .2500 #7 .2010 1/4-26 .2500 #4 .2090 1/4-28 .2500 #3 .2130 7-1.0 .2756 6.0 mm .2362 15/64 .2344 5/16-18 .3125 1/4 .2500 5/16-18 .3125 F .2570 5/16-22 .3125 G .2610 5/16-24 .3125 I (i) .2720 5/16-26 .3125 J .2770 8-1.0 .3150 7.0 mm .2756 I (i) .2720 8-1.25 .3150 6.8 mm .2677 H .2660 3/8-16 .3750 5/16 .3125 3/8-16 .3750 5/16 .3125 3/8-20 .3750 P .3230 3/8-24 .3750 Q .3320 3/8-26 .3750 Q .3320 10-1.5 .3937 8.5 mm .3346 Q .3320 10-1.25 .3973 8.8 mm .3465 S .3480 10-1.0 .3973 9.0 mm .3543 S .3480 7/16-14 .4375 23/64 .3594 7/16-14 .4375 U .3680 7/16-18 .4375 3/8 .3750 7/16-20 .4375 25/64 .3906 7/16-26 .4375 Y .4040 12-1.75 .4724 10.3 mm .4055 Y .4040 12-1.5 .4724 10.5 mm .4134 Z .4130 12-1.25 .4724 10.8 mm .4252 27/64 .4219 12-1.0 .4724 11.0 mm .4331 7/16 .4375 1/2-12 .5000 13/32 .4062 1/2-13 .5000 27/64 .4219 1/2-20 .5000 7/16 .4375 1/2-20 .5000 29/64 .4531 1/2-26 .5000 29/64 .4531 14-2.0 .5512 12.0 mm .4724 15/32 .4688 14-1.75 .5512 12.3 mm .4842 31/64 .4844 14-1.5 .5512 12.5 mm .4921 1/2 .5000 14-1.25 .5512 12.8 mm .5039 1/2 .5000 14-1.0 .5512 13.0 mm .5118 33/64 .5156