Double Depth of Screw Threads ISO External Threads MEDIUM FIT Millimeter Standard p = distance between any point on a thread to the corresponding point on the adjacent thread d = depth – 0.64952P f = flat – 0.125P p d f f 60º D.D. = 1.732 For V Thread N D.D. = 1.299 For American Nat. Form, U.S. Std N D.D. = 1.28 For Whitworth Standard N Threads per Inch V Threads Am. Nat. Form U.S. Standard Whitworth Standard N D.D. D.D. D.D. 2 .86600 .64950 .64000 3 .57733 .43300 .42666 4 .43300 .32475 .32000 10 .17320 .12990 .12800 13 .13323 .09992 .09846 18 .09622 .07216 .07111 20 .08660 .06495 .06400 22 .07872 .05904 .05818 24 .07216 .05412 .05333 26 .06661 .04996 .04923 27 .06415 .04811 .04740 28 .06185 .04639 .04571 30 .05773 .04330 .04266 32 .05412 .04059 .04000 34 .05094 .03820 .03764 36 .04811 .03608 .03555 38 .04558 .03418 .03368 40 .04330 .03247 .03200 56 .03093 .02319 .02285 60 .02887 .02165 .02133 80 .02165 .01623 .01600 Designation mm Diameter mm Pitch M2 x 0.4 2 0.4 M3 x 0.5 3 0.5 M4 x 0.7 4 0.7 M5 x 0.8 5 0.8 M6 x 1 6 1.0 M8 x 1.25 8 1.25 M10 x 1.5 10 1.5 M12 x 1.75 12 1.75 M16 x 2 16 2.0 M20 x 2.5 20 2.5 M24 x 3 24 3.0 M30 x 3.5 30 3.5 Thread Terminology Angle Root Crest Pitch Pitch/2 F l a n k Major Diameter Pitch Diameter Minor Diameter 584 R eference T ables