American National Standard Pipe Thread standards, often called national pipe thread standards for short, are United States national technical standards for screw threads used on threaded pipes and pipe fittings. They include both tapered and straight thread series for various purposes, including rigidity, pressure-tight sealing, or both. The types are named with a full name and an abbreviation, such as NPT, NPS, NPTF, or NPSC.
| NPT ‐ National Pipe Thread Taper ‐ ANSI B1.20.1 | |||||
| Pipe Size | Threads/Inch | Approx. Length of Thread | Approx. Number of Threads to be cut | Nominal Outside Pipe Diameter | Tap Drill |
| 1/8" | 27 | 3/8" | 10 | 0.405" | |
| 1/4" | 18 | 5/8" | 11 | 0.540" | 7/16" |
| 3/8" | 18 | 5/8" | 11 | 0.675" | 37/64" |
| 1/2" | 14 | 3/4" | 10 | 0.840" | 23/32" |
| 3/4" | 14 | 3/4" | 10 | 1.050" | 59/64" |
| 1" | 11‐1/2 | 7/8" | 10 | 1.315" | 1‐5/32" |
| 1‐1/4" | 11‐1/2 | 1" | 11 | 1.660" | 1‐1/2" |
| 1‐1/2" | 11‐1/2 | 1" | 11 | 1.900" | 1‐47/64" |
| 2" | 11‐1/2 | 1" | 11 | 2.375" | 2‐7/32" |
| 2‐1/2" | 8 | 1‐1/2" | 12 | 2.875" | 2‐5/8" |