NPT - National Pipe Taper
3/4 Taper(Dry Seal). A dry seal has a 3/4" taper per 12" and designed to have its threads mesh tightly with those of a taper threaded hole
7/8 Taper(Flush Seal). A flush seal has a 7/8" taper per 12" and is designed to provide a flush condition with standard tapped hole.
| Screw Size | Decimal | Pitch | Tap Drill |
|---|---|---|---|
| 1/16 | 0.0625 | 27 | D |
| 1/8 | 0.1250 | 27 | R |
| 1/4 | 0.2500 | 18 | 7/16 |
| 3/8 | 0.3750 | 18 | 37/64 |
| 1/2 | 0.5000 | 14 | 45/64 |
| 3/4 | 0.7500 | 14 | 29/32 |
| 1 | 1.0000 | 11 1/2 | 1 9/64 |
| 1 1/4 | 1.2500 | 11 1/2 | 1 1/2 |
| 1 1/2 | 1.5000 | 11 1/2 | 1 47/64 |
| 2 | 2.0000 | 11 1/2 | 2 7/32 |
NPS - National Pipe Straight
| Screw Size | Decimal | Pitch | Tap Drill |
|---|---|---|---|
| 1/8 | 0.1250 | 27 | S |
| 1/4 | 0.2500 | 18 | 29/64 |
| 3/8 | 0.3750 | 18 | 19/32 |
| 1/2 | 0.5000 | 14 | 47/64 |
| 3/4 | 0.7500 | 14 | 15/16 |
| 1 | 1.0000 | 11 1/2 | 1 3/16 |
| 1 1/4 | 1.2500 | 11 1/2 | 1 33/64 |
| 1 1/2 | 1.5000 | 11 1/2 | 1 3/4 |
| 2 | 2.0000 | 11 1/2 | 2 7/32 |