| BSF Standard Threads and Tapping Drills | ||||||||||||
| Dimensions in inches | Flank angle 55 deg. | Drill sizes | ||||||||||
| Tapping | Clearance | |||||||||||
| Overall diameter | Core dia. | Effective dia. | Thread form | Teeth per inch | BSI recommended | BSI alternate | ||||||
| fraction | decimal | Depth | Radius | mm/in. | dec. in | mm/in. | dec. in | mm/in. | dec. in | |||
| 3/16 | 0.1875 | 0.1475 | 0.1675 | 0.0200 | 0.0046 | 32 | 5/32" | 0.1563 | 3.95 | 0.1555 | 4.90 | 0.1929 |
| 7/32 | 0.2188 | 0.1730 | 0.1959 | 0.0229 | 0.0049 | 28 | 4.65 | 0.1831 | 4.60 | 0.1811 | 5.60 | 0.2205 |
| 1/4 | 0.2500 | 0.2008 | 0.2254 | 0.0246 | 0.0053 | 26 | 5.30 | 0.2087 | 5.25 | 0.2067 | 6.50 | 0.2559 |
| 5/16 | 0.3125 | 0.2543 | 0.2834 | 0.0291 | 0.0062 | 22 | 6.75 | 0.2657 | 17/64" | 0.2656 | 8.00 | 0.3150 |
| 3/8 | 0.3750 | 0.3110 | 0.3430 | 0.0320 | 0.0069 | 20 | 8.25 | 0.3248 | 8.20 | 0.3228 | 9.80 | 0.3858 |
| 7/16 | 0.4375 | 0.3663 | 0.4019 | 0.0356 | 0.0076 | 18 | 9.70 | 0.3819 | 9.60 | 0.3780 | 29/64" | 0.4531 |
| 1/2 | 0.5000 | 0.4200 | 0.4600 | 0.0400 | 0.0086 | 16 | 7/16" | 0.4375 | 11.10 | 0.4370 | 33/64" | 0.5156 |
| 9/16 | 0.5625 | 0.4825 | 0.5225 | 0.0400 | 0.0086 | 16 | 1/2" | 0.5000 | 12.60 | 0.4961 | 37/64" | 0.5781 |
| 5/8 | 0.6250 | 0.5336 | 0.5793 | 0.0457 | 0.0098 | 14 | 14.00 | 0.5512 | 35/64" | 0.5469 | 41/64" | 0.6406 |
| 3/4 | 0.7500 | 0.6432 | 0.6966 | 0.0534 | 0.0114 | 12 | 16.75 | 0.6594 | 21/32 | 0.6563 | 49/64" | 0.7656 |
| 7/8 | 0.8750 | 0.7586 | 0.8168 | 0.0582 | 0.0125 | 11 | 25/32" | 0.7813 | 19.75 | 0.7776 | 57/64" | 0.8906 |
| 1 | 1.0000 | 0.8720 | 0.9360 | 0.0640 | 0.0137 | 10 | 22.75 | 0.8957 | 57/64" | 0.8906 | 1 1/64" | 1.0156 |
| 1 1/8 | 1.1250 | 0.9828 | 1.0539 | 0.0711 | 0.0153 | 9 | 25.50 | 1.0039 | 1" | 1.0000 | 1 9/64" | 1.1406 |
| 1 1/4 | 1.2500 | 1.1078 | 1.1789 | 0.0711 | 0.0153 | 9 | 28.75 | 1.1319 | 1 1/8" | 1.1250 | 1 17/64" | 1.2656 |
| 1 3/8 | 1.3750 | 1.2150 | 1.2950 | 0.0800 | 0.0172 | 8 | 31.50 | 1.2402 | 1 15/64" | 1.2344 | 1 25/64" | 1.3906 |
| 1 1/2 | 1.5000 | 1.3400 | 1.4200 | 0.0800 | 0.0172 | 8 | 1 23/64" | 1.3594 | 34.50 | 1.3583 | 1 33/64" | 1.5156 |
| 1 5/8 | 1.6250 | 1.4649 | 1.5450 | 0.0801 | 0.0172 | 8 | ||||||
| 1 3/4 | 1.7500 | 1.5670 | 1.6585 | 0.0915 | 0.0196 | 7 | ||||||
| 2 | 2.0000 | 1.8170 | 1.9085 | 0.0915 | 0.0196 | 7 | ||||||
| 2 1/4 | 2.2500 | 2.0366 | 2.1433 | 0.1067 | 0.0229 | 6 | ||||||
| 2 1/2 | 2.5000 | 2.2866 | 2.3933 | 0.1067 | 0.0229 | 6 | ||||||
| 2 3/4 | 2.7500 | 2.5366 | 2.6433 | 0.1067 | 0.0229 | 6 | ||||||
| 3 | 3.0000 | 2.7439 | 2.8720 | 0.1281 | 0.0275 | 5 | ||||||