Tapers and Angles American St andard Acme Screw Thread Dimensions p h' Fr Fc 29º h = Basic depth of thread h' = Depth of thread with clearance K = Tap drill Basic minor diameter of nut Fc = Width of flat at crest of thread Fr = Width of flat at bottom of space n = Number of threads per inch p = Pitch of thread Kr = Minor diameter of screw D = Major diameter of screw T = Major diameter of tap FOR 10 OR FEWER THREADS PER INCH h' = P plus .010 2 Fr = .3707 minus .0052 n T = D plus .020 FOR MORE THAN 10 THREADS PER INCH h' = P plus .005 2 Fr = .3707 minus .0026 n T = D plus .010 p = 1 Fc = .3707 n n K = D minus p Kr = D minus 2h' Threads per inch (n) Depth of Thread with Clearance (h') Flat at Top of Thread (Fc) Flat at Bottom of Space (Fr) Space at Top of Thread Thickness at Root of Thread 1 .5100 .3707 .3655 .6293 .6345 1-1/3 .3850 .2780 .2728 .4720 .4772 2 .2600 .1854 .1802 .3146 .3198 3 .1767 .1236 .1184 .2097 .2149 4 .1350 .0927 .0875 .1573 .1625 5 .1100 .0741 .0689 .1259 .1311 6 .0933 .0618 .0566 .1049 .1101 7 .0814 .0530 .0478 .0899 .0951 8 .0725 .0463 .0411 .0787 .0839 9 .0655 .0412 .0360 .0699 .0751 10 .0600 .0371 .0319 .0629 .0681 12 .0467 .0309 .0283 .0524 .0550 14 .0407 .0265 .0239 .0449 .0475 16 .0363 .0232 .0206 .0393 .0419 Taper per Foot Degree Included Angle Minute Second Degree Angle With Center Line Minute Second Taper per inch Taper per inch from Center Line 1/8" 0 35 49 0 17 54 .010417 .005208 1/4" 1 11 37 0 35 49 .020833 .010417 3/8" 1 47 25 0 53 43 .031250 .015625 1/2" 2 23 13 1 11 37 .041667 .020833 5/8" 2 59 1 1 29 30 .052083 .026042 3/4" 3 34 47 1 47 24 .062500 .031250 7/8" 4 10 33 2 5 17 .072917 .036458 1" 4 46 19 2 23 9 .083333 .041667 1-1/4" 5 57 47 2 58 53 .104167 .052084 1-1/2" 7 9 10 3 34 35 .125000 .062500 1-3/4" 8 20 27 4 10 14 .145833 .072917 2" 9 31 38 4 45 49 .166667 .083333 2-1/2" 11 53 37 5 56 49 .208333 .104167 3" 14 2 0 7 1 30 .250000 .125000 3-1/2" 16 35 39 8 17 50 .291667 .145833 4" 18 55 29 9 27 44 .333333 .166667 4-1/2" 21 14 22 10 37 11 .375000 .187500 5" 23 32 12 11 46 6 .416667 .208333 6" 28 4 21 14 2 10 .500000 .250000 585 starrett.com R eference T ables