Size(mm) Size(in) Fraction(in)Letter or Number Description 0.2 0.0079 ...................... 0.22 0.0087 ...................... 0.25 0.0098 ...................... 0.28 0.0110 ...................... 0.3 0.0118 ...................... 0.32 0.0126 ...................... 0.35 0.0138 80 ...................... 0.38 0.0150 79 ...................... 0.39 0.0156 1/64 ...................... 0.4 0.0157 78 ...................... 0.42 0.0165 ...................... 0.45 0.0177 77 ...................... 0.48 0.0189 ...................... 0.5 0.0197 76 ...................... 0.52 0.0205 75 ...................... 0.55 0.0217 ...................... 0.58 0.0228 74 ...................... 0.6 0.0236 73 Tapping Drill 16 BA 0.62 0.0244 72 ...................... 0.65 0.0256 71 ...................... 0.68 0.0268 ...................... 0.7 0.0276 70 Tapping Drill 15 BA 0.72 0.0283 ...................... 0.75 0.0295 69 Tapping Drill ISO metric coarse 1 mm 0.78 0.0307 ...................... 0.79 0.0312 1/32 68 ...................... 0.8 0.0315 Tapping Drill 14 BA 0.82 0.0323 67 ...................... 0.85 0.0335 66 Tapping Drill ISO Metric Coarse 1.1 mm 0.88 0.0346 ...................... 0.9 0.0354 65 ...................... 0.92 0.0362 64 ...................... 0.95 0.0374 63 Tapping Drill ISO Metric Coarse 1.2 mm 0.98 0.0386 62 Tapping Drill 13 BA 1 0.0394 61 Tapping Drill 12 BA and 17swg CEI 1.05 0.0413 60 Tapping Drill 12 BA 1.1 0.0433 59 Tapping Dnll ISO Metric Coarse 1.4 mm 1.15 0.0453 58 ...................... 1.19 0.0469 3/64 57 Tapping Drill 16swg CEI 1.2 0.0472 56 Tapping Drill 11 BA and 1/16 Whitworth 1.25 0.0492 Tapping Dnll ISO Metric Coarse 1.6 mm and No 0 UNF 1.3 0.0512 55 ...................... 1.35 0.0531 Tapping Drill ISO Metric Special Pitches 1.7 mm 1.4 0.0551 54 Tapping Drill 15swg CEI and 10BA 1.45 0.0571 Tapping Drill ISO Metric Coarse 1.8 mm 1.5 0.0591 53 Tapping Drill 9 BA 1.55 0.0610 Tapping Drill ISO Metric Special Pitches 2 mm and No1 UNC 1.58 0.0625 1/16 ...................... 1.6 0.0630 52 Tapping Drill ISO Metric Coarse 2 mm, No1 UNF and 14swg CEI 1.65 0.0650 ...................... 1.7 0.0669 51 ...................... 1.75 0.0689 Tapping Drill ISO Metric Coarse 2.2 mm 1.8 0.0709 50 Tapping Drill 8 BA 1.85 0.0728 49 Tapping Drill 3/32 Whitworth, No2 UNC and 13swg CEI 1.9 0.0748 48 Tapping Drill ISO Metric Special Pitches 2.3 mm and No2 UNF 1.95 0.0768 ...................... 1.98 0.0781 5/64 ...................... 2 0.0787 47 Tapping Drill 7 BA 2.05 0.0807 46 Tapping Drill ISO Metric Coarse 2.5 mm and 12swg CEI 2.1 0.0827 45 Tapping Drill No3 UNC 2.15 0.0846 Tapping Drill ISO Metric Special Pitches 2.6 mm and No3 UNF 2.2 0.0866 44 ...................... 2.25 0.0886 43 ...................... 2.3 0.0906 Tapping Drill 6 BA 2.35 0.0925 Tapping Drill No4 UNC 2.38 0.0938 3/32 42 ...................... 2.4 0.0945 Tapping Drill ISO Metric Special Pitches 3 mm and No4 UNF 2.45 0.0965 41 ...................... 2.5 0.0984 40 Tapping Drill ISO Metric Coarse 3 mm 2.55 0.1004 39 Tapping Drill 1/8 Whitworth 1/8 BSC and 1/8 CEI 2.6 0.1024 38 Tapping Drill 5 BA 2.65 0.1043 37 Tapping Drill ISO Metric Fine 3 mm and No5 UNC 2.7 0.1063 36 Tapping Drill No5 UNF 2.75 0.1083 ...................... 2.78 0.1094 7/64 ...................... 2.8 0.1102 35 ...................... 2.85 0.1122 34 Tapping Drill No6 UNC 2.9 0.1142 33 Tapping Drill ISO Metric Coarse 3.5 mm 2.95 0.1161 32 Tapping Drill 4 BA and No6 UNF 3 0.1181 31 ...................... 3.1 0.1220 ...................... 3.18 0.1250 1/8 ...................... 3.2 0.1260 30 Tapping Drill 5/32 BSC, 5/32 Whitworth, ISO Metric Special Pitches 2.3 mm and 0.154 CEI 3.3 0.1299 Tapping Drill ISO Metric Coarse 4 mm 3.4 0.1339 29 Tapping Drill 3 BA 3.5 0.1378 Tapping Drill ISO Metric Fine 4 mm and No8 UNC 3.55 0.1398 Tapping Drill No8 UNF 3.57 0.1406 9/64 28 ...................... 3.6 0.1417 27 Tapping Drill 0.175 CEI 3.7 0.1457 26 Tapping Drill 3/16 Whitworth 3.8 0.1496 25 Tapping Drill ISO Metric Coarse 4.5 mm 3.9 0.1535 24 Tapping Drill No10 UNC 3.97 0.1562 5/32 23 Tapping Drill 3/16 BSF 3/16 CEI and 3/16 BSC 4 0.1575 22 Tapping Drill 2 BA 4.1 0.1614 21 Tapping Drill ISO Metric Special Pitches 5 mm and No 10 UNF 4.2 0.1654 20 Tapping Drill ISO Metric Coarse 5 mm 4.3 0.1693 19 ...................... 4.37 0.1719 11/64 18 ...................... 4.4 0.1732 17 ...................... 4.5 0.1772 16 Tapping Drill 1 BA, 7/32 Whitworth, and ISO Metric Fine 5 mm 4.55 0.1791 Tapping Drill No12 UNC 4.6 0.1811 15 Tapping Drill 7/32 BSF and ISO Metric Special Pitches 5.5 mm 4.65 0.1831 Tapping Drill No 12 UNF 4.7 0.1850 14 ...................... 4.76 0.1875 3/16 13 ...................... 4.8 0.1890 12 ...................... 4.9 0.1929 11 ...................... 5 0.1969 10 Tapping Drill ISO Metric Coarse 6 mm 5.1 0.2008 9 Tapping Drill 0 BA and 1/4 Whitworth 5.16 0.2031 13/64 8 ...................... 5.2 0.2047 7 Tapping Drill 1/4 UNC and ISO Metric Fine 6 mm 5.3 0.2087 6 Tapping Drill 1/4 BSF 5.4 0.2126 5 ...................... 5.5 0.2165 4 Tapping Drill 1/4 UNF 5.56 0.2188 7/32 3 Tapping Drill 1/4 BSC and 1/4 CEI 5.6 0.2205 2 ...................... 5.7 0.2244 ...................... 5.8 0.2283 1 Tapping Drill 0.266 CEI 5.9 0.2323 A ...................... 5.95 0.2344 15/64 ...................... 6 0.2362 B Tapping Drill ISO Metric Coarse 7 mm and 9/32 BSF 6.1 0.2402 C ...................... 6.2 0.2441 D Tapping Drill 9/32 BSC, 0.281 CEI and ISO Metric Fine 7 mm 6.3 0.2480 E ...................... 6.35 0.2500 1/4 ...................... 6.4 0.2520 Tapping Drill 1/16 BSTP 6.5 0.2559 F Tapping Drill 5/16 Whitworth 6.6 0.2598 G Tapping Drill 5/16 UNC and 1/16 BSP 6.7 0.2638 H ...................... 6.75 0.2655 17/64 Tapping Drill 5/16 BSF 6.8 0.2677 Tapping Drill ISO Metric Coarse 8 mm 6.9 0.2717 I Tapping Drill 5/16 UNF 7 0.2756 J Tapping Drill 5/16 BSC, ISO Metric Fine 8 mm and 5/16 CEI 7.1 0.2795 K ...................... 7.14 0.2812 9/32 ...................... 7.2 0.2835 Tapping Drill ISO Metric Special Pitches 8 mm 7.3 0.2874 L ...................... 7.4 0.2913 M ...................... 7.5 0.2953 ...................... 7.54 0.2969 19/64 ...................... 7.6 0.2992 N ...................... 7.7 0.3031 ...................... 7.8 0.3071 Tapping Dnll ISO Metric Coarse 9 mm 7.9 0.3110 ...................... 7.94 0.3125 5/16 Tapping Drill 3/8 Whitworth 8 0.3150 0 Tapping Drill 3/8 UNC and ISO Metric Special Pitches 9 mm 8.1 0.3189 ...................... 8.2 0.3228 P Tapping Drill 3/8 BSF 8.3 0.3268 ...................... 8.33 0.3281 21/64 ...................... 8.4 0.3307 Q Tapping Drill 1/8 BSTP 8.5 0.3346 Tapping Drill ISO Metric Coarse 10 mm and 3/8 UNF 8.6 0.3386 R Tapping Drill 3/8 BSC and 3/8 CEI 8.7 0.3425 ...................... 8.73 0.3438 11/32 Tapping Drill 1/8 BSP 8.8 0.3465 5 Tapping Drill ISO Metric Fine 10 mm 8.9 0.3504 ...................... 9 0.3543 Tapping Drill ISO Metric Special Pitches 10 mm 9.1 0.3583 T ...................... 9.13 0.3594 23/64 ...................... 9.2 0.3622 Tapping Drill ISO Metric Special Pitches 10 mm 9.3 0.3661 U Tapping Drill 7/16 Whitworth 9.4 0.3701 Tapping Drill 7/16 UNC 9.5 0.3740 V Tapping Dnll ISO Metric Coarse 11 mm 9.53 0.3750 3/8 ...................... 9.6 0.3780 ...................... 9.7 0.3819 Tapping Drill 7/16 BSF 9.8 0.3858 W ...................... 9.9 0.3898 Tapping Drill 7/16 UNF 9.92 0.3906 25/64 ...................... 10 0.3937 ...................... 10.1 0.3976 X Tapping Drill 7/16 BSC 10.2 0.4016 Tapping Drill ISO Metric Coarse 12 mm 10.3 0.4055 Y ...................... 10.32 0.4062 13/32 ...................... 10.4 0.4094 ...................... 10.5 0.4134 Z Tapping Drill 1/2 Whitworth and ISO Metric Special Pitches 12 mm (1.5 mm pitch) 10.6 0.4173 ...................... 10.7 0.4213 ...................... 10.72 0.4219 27/64 ...................... 10.8 0.4252 Tapping Drill 1/2 UNC and ISO Metric Fine 12 mm 10.9 0.4291 ...................... 11 0.4331 Tapping Drill ISO Metric Special Pitches 12 mm (1mm pitch) 11.1 0.4370 ...................... 11.11 0.4375 7/16 Tapping Drill 1/2 BSF 11.2 0.4409 Tapping Drill 1/4 BSTP 11.3 0.4449 ...................... 11.4 0.4488 Tapping Drill 1/2 UNF 11.5 0.4528 ...................... 11.51 0.4531 29/64 ...................... 11.6 0.4567 ...................... 11.7 0.4606 ...................... 11.8 0.4646 Tapping Drill 1/4 BSP 11.9 0.4685 ...................... 11.91 0.4688 15/32 ...................... 12 0.4724 Tapping Drill ISO Metric Coarse 14 mm 12.1 0.4764 Tapping Drill 9/16 Whitworth 12.2 0.4803 Tapping Drill 9/16 UNC 12.3 0.4843 ...................... 12.3 0.4844 31/64 ...................... 12.4 0.4882 ...................... 12.5 0.4921 Tapping Drill ISO Metric Special Pitches 14 mm 12.6 0.4961 ...................... 12.7 0.5000 1/2 Tapping Drill 9/16 BSF 12.8 0.5039 Tapping Drill ISO Metric Fine 14 mm 12.9 0.5079 Tapping Drill 9/I 6 UNF 13 0.5118 ...................... 13.1 0.5156 33/64 Tapping Drill 9/16 BSC and 9/16 CEI 13.1 0.5157 ...................... 13.2 0.5197 ...................... 13.3 0.5236 ...................... 13.4 0.5276 ...................... 13.49 0.5313 17/32 Tapping Drill 5/8 UNC 13.5 0.5315 Tapping Drill 5/8 Whitworth 13.6 0.5354 ...................... 13.7 0.5394 ...................... 13.8 0.5433 ...................... 13.89 0.5469 35/64 ...................... 13.9 0.5472 ...................... 14 0.5512 Tapping Drill ISO Metric Coarse 16 mm and 5/8 BSF 14.25 0.5610 ...................... 14.3 0.5625 9/16 ...................... 14.5 0.5709 Tapping Drill 5/8 UNF and ISO Metric Fine 16 mm 14.68 0.5780 37/64 ...................... 14.75 0.5807 Tapping Drill 3/8 BSTP 15 0.5906 Tapping Drill 11/16 Whitworth, ISO Metric Special Pitches 16 mm and 5/8 BSC 15.08 0.5937 19/32 ...................... 15.25 0.6004 Tapping Drill 3/8 BSP 15.48 0.6094 39/64 ...................... 15.5 0.6102 Tapping Drill ISO Metric Coarse 18 mm and 11/16 BSF 15.75 0.6201 ...................... 15.88 0.6252 5/8 ...................... 16 0.6299 ...................... 16.25 0.6398 ...................... 16.27 0.6406 41/64 Tapping Drill 3/4 Whitworth 16.5 0.6496 Tapping Drill 3/4 UNC and ISO Metric Fine 18 mm 16.67 0.6563 21/32 ...................... 16.75 0.6594 Tapping Drill 3/4 BSF 17 0.6693 ...................... 17.07 0.6720 43/64 ...................... 17.25 0.6791 ...................... 17.46 0.6874 11/16 Tapping Drill 3/4 UNF 17.5 0.6890 Tapping Drill ISO Metric Coarse 20 mm 17.75 0.6988 ...................... 17.86 0.7031 45/64 ...................... 18 0.7087 Tapping Drill 13/16 Whitworth and ISO Metric Special Pitches 20 mm (2 mm pitch) 18.25 0.7185 Tapping Drill 1/2 BSTP 18.26 0.7189 23/32 ...................... 18.5 0.7283 Tapping Drill ISO Metric Fine 20 mm 18.65 0.7343 47/64 ...................... 18.75 0.7382 ...................... 19 0.7480 Tapping Drill ISO Metric Special Pitches 20 mm (1 mm pitch) 19.05 0.7500 3/4 Tapping Drill 1/2 BSP 19.25 0.7579 Tapping Drill 7/8 Whitworth 19.45 0.7656 49/64 Tapping Drill 7/8 UNC 19.5 0.7677 Tapping Drill ISO Metric Coarse 22 mm 19.75 0.7776 ...................... 19.84 0.7812 25/32 Tapping Drill 7/8 BSF 20 0.7874 ...................... 20.24 0.7969 51/64 ...................... 20.25 0.7972 ...................... 20.5 0.8071 Tapping Drill ISO Metric Fine 22 mm 20.64 0.8125 13/16 Tapping Drill 7/8 UNF 20.75 0.8169 Tapping Drill 15/16 Whitworth 21 0.8268 Tapping Drill ISO Metric Coarse 24 mm 21.03 0.8281 53/64 Tapping Drill 5/8 BSP 21.25 0.8366 ...................... 21.43 0.8438 27/32 ...................... 21.5 0.8465 ...................... 21.75 0.8563 ...................... 21.83 0.8594 55/64 ...................... 22 0.8661 Tapping Drill 1 inch Whitworth and ISO Metric Fine 24 mm 22.23 0.8750 7/8 ...................... 22.25 0.8760 Tapping Drill I UNC 22.5 0.8858 Tapping Drill ISO Metric Special Pitches 24 mm (1.5 mm pitch) 22.62 0.8906 57/64 ...................... 22.75 0.8957 Tapping Drill 1 inch BSF 23 0.9055 Tapping Drill ISO Metric Special Pitches 24 mm (1 mm pitch) 23.02 0.9062 29/32 ...................... 23.25 0.9154 Tapping Drill I inch UNF 23.42 0.9219 59/64 ...................... 23.5 0.9252 Tapping Drill ISO Metric Special Pitches 25 mm (1.5 mm pitch) 23.75 0.9350 Tapping Drill 3/4 BSTP 23.81 0.9375 15/16 ...................... 24 0.9449 Tapping Drill ISO Metric Coarse 27 mm 24.21 0.9531 61/64 ...................... 24.25 0.9547 ...................... 24.5 0.9646 Tapping Drill 3/4 BSP 24.61 0.9688 31/32 Tapping Drill 1inch BSC and 1 inch CEI 24.75 0.9744 ...................... 25 0.9843 Tapping Drill ISO Metric Fine 27 mm 25 0.9844 63/64 ...................... 25.4 1.0000 1 ...................... Standards rise in Increments of 1/64in and 0.50 mm.