Unified inch threads. USS/Coarse is UNC and SAE/Fine is UNF. Tap drills are for about 75% thread.
| Size | Diameter (in) | Coarse TPI (UNC) | Coarse tap drill | Fine TPI (UNF) | Fine tap drill |
|---|---|---|---|---|---|
| #0 | 0.060 | 80 | 3/64 | ||
| #1 | 0.073 | 64 | #53 | 72 | #53 |
| #2 | 0.086 | 56 | #50 | 64 | #50 |
| #3 | 0.099 | 48 | #47 | 56 | #45 |
| #4 | 0.112 | 40 | #43 | 48 | #42 |
| #5 | 0.125 | 40 | #38 | 44 | #37 |
| #6 | 0.138 | 32 | #36 | 40 | #33 |
| #8 | 0.164 | 32 | #29 | 36 | #29 |
| #10 | 0.190 | 24 | #25 | 32 | #21 |
| #12 | 0.216 | 24 | #16 | 28 | #14 |
| 1/4 | 0.250 | 20 | #7 | 28 | #3 |
| 5/16 | 0.3125 | 18 | F | 24 | I |
| 3/8 | 0.375 | 16 | 5/16 | 24 | Q |
| 7/16 | 0.4375 | 14 | U | 20 | 25/64 |
| 1/2 | 0.500 | 13 | 27/64 | 20 | 29/64 |
| 9/16 | 0.5625 | 12 | 31/64 | 18 | 33/64 |
| 5/8 | 0.625 | 11 | 17/32 | 18 | 37/64 |
| 3/4 | 0.750 | 10 | 21/32 | 16 | 11/16 |
| 7/8 | 0.875 | 9 | 49/64 | 14 | 13/16 |
| 1 | 1.000 | 8 | 7/8 | 12 | 59/64 |
| 1-1/8 | 1.125 | 7 | 63/64 | 12 | 1-3/64 |
| 1-1/4 | 1.250 | 7 | 1-7/64 | 12 | 1-11/64 |
| 1-3/8 | 1.375 | 6 | 1-7/32 | 12 | 1-19/64 |
| 1-1/2 | 1.500 | 6 | 1-11/32 | 12 | 1-27/64 |
| 1-3/4 | 1.750 | 5 | 1-9/16 | ||
| 2 | 2.000 | 4-1/2 | 1-25/32 |
Reading inch sizes
A size like 1/2-13 x 2 means 1/2" diameter, 13 threads per inch, 2" long. Part numbers ending in -F are fine thread.