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Besly Drill Selector for Modern Application Taps
Metric Sizes*
UNC/UNF Threads
ASME B1.13M-1995
Tap Size and Pitch MM
Drill Size Min. Hole Size
(for nickel and
titanium alloys)
M3 x .5 38 .1015
M3.5 x .6 32 .1160
M4 x .7 3.40mm .1339
M4 x .5 9/64 .1406
M5 x .8 18 .1695
M5 x .5 15 .1800
M6 x 1 7 .2010
M6 x .75 4 .2090
M7 x 1 B .2380
M8 x 1.25 I .2720
M8 x 1 J ..2770
M9 x 1.25 7.80mm .3071
M10 x 1.5 R .3390
M10 x 1.25 S .3480
M10 x 1 T .3580
M11 x 1.5 V .3770
M12 x 1.75 13/32 .4062
M12 x 1.5 10.60mm .4173
M12 x 1.25 10.80mm .4252
M12 x 1 7/16 .4375
M14 x 2 12.10mm .4764
M14 x 1.5 12.60mm .4961
M15 x 1 14mm .5551
M16 x 2 14mm .5551
M16 x 1.5 14.60mm .5748
M17 x 1 16.10mm .6339
M18 x 1.25 15.70mm .6181
M18 x 1.5 16.50mm .6496
M20 x 2.5 17.70mm .6968
M20 x 1.5 47/64 .7344
M20 x 1 3/4 .7500
M22 x 2.5 19.70mm .7756
M22 x 2 20.10mm .7913
M22 x 1.5 13/16 .8125
M24 x 3 21.20mm .8346
M24 x 2 22.10mm .8700
M25 x 1.5 23.50mm .9252
* Principle factors which influence the minor diameter tolerance are ease of tapping, standard drill sizes, and height of engagement. When tapping difficult-to-machine materials, the height of engagement may be shallower and still develop stripping strength greater than the external thread breaking strength. In these instances, the minor diameter may be increased to the maximum tolerance to reduce the possibility of tapping difficulties.

Refer to the following publications for specific information on limiting dimensions for internal screw threads:
 ●  ASME B1.13M-1995, METRIC SCREW THREADS-M PROFILE.
 ●  FED-STD-H28, FEDERAL STANDARD SCREW-THREAD STANDARDS FOR FEDERAL SERVICES.
 ●  DRILLED HOLES FOR TAPPING BY THE UNITED STATES CUTTING TOOL INSTITUTE

 

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