NPT– (National Pipe Taper)
| TAP SIZE | DRILL SIZE |
| 1/8-27 NPT | R (0.339) |
| 1/4-18 NPT | 7/16″ (0.4375) |
| 3/8-18 NPT | 37/64″ (0.578) |
| 1/2-14 NPT | 23/32″ (.719) |
| 3/4-14 NPT | 59/64″ (0.923) |
| 1-11.5 NPT | 1-5/32″ (1.156) |
| 1 1/4-11.5 NPT | 1 1/2″ (1.500) |
| 1 1/2-11.5 NPT | 1 47/64″ (1.734) |
| 2-11-1.5 NPT | 2-7/32″ (2.219) |
| 2 1/2-8 NPT | 2-5/8″ (2.625) |
| 3-8 NPT | 3-1/4″ (3.250) |
| 3 1/2-8 NPT | 3-3/4″ (3.750) |
| 4-8 NPT | 4-1/4″ (4.250) |
NPS (National Pipe Straight)
| TAP SIZE | DRILL SIZE |
| 1/8-27 NPT | S (0.348) |
| 1/4-18 NPT | 29/64″ (0.453) |
| 3/8-18 NPT | 19/32″ (0.594) |
| 1/2-14 NPT | 47/64″ (0.734) |
| 3/4-14 NPT | 15/16″ (0.9375) |
| 1-11.5 NPT | 1-3/16″ (1.1875) |
| 1 1/4-11.5 NPT | 1-33/64″ (1.515) |
| 1 1/2-11.5 NPT | 1 3/4″ (1.750) |
| 2-11-1.5 NPT | 2-7/32″ (2.219) |
| 2 1/2-8 NPT | 2-21/32″ (2.656) |
| 3-8 NPT | 3-9/32″ (3.281) |
| 3 1/2-8 NPT | 3-25/32″ (3.781) |
| 4-8 NPT | 4-9/32″ (4.281) |