For npt pipe thread fittings, ASME B1.20.1 is the governing document for the dimensions listed below. Mechanical and performance requirements for this part family are set by its own standards, not by the bolt and screw property-class documents.
ASME B1.20.1 — Scope
ASME B1.20.1 is "Pipe threads, general purpose (inch)". The NPT taper pipe thread document.
This document is not a dimensional standard. The table on this page comes from the catalogue entry for the part, not from it.
Tolerance & Product Grades
Product grade is a concept from dimensional fastener standards and does not apply to ASME B1.20.1. Tolerances for this part are the limits shown against each dimension in the table.
Dimensions Specified by ASME B1.20.1
| Size | Nominal size (in) | Major diameter (mm) | Pitch (mm) | Threads per inch (TPI) | Taper | Reference standard | Notes |
|---|---|---|---|---|---|---|---|
| 1/16 NPT | 1/16 | 7.938 | 0.941 | 27 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 1/8 NPT | 1/8 | 10.287 | 0.941 | 27 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 1/4 NPT | 1/4 | 13.716 | 1.411 | 18 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 3/8 NPT | 3/8 | 17.145 | 1.411 | 18 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 1/2 NPT | 1/2 | 21.336 | 1.814 | 14 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 3/4 NPT | 3/4 | 26.67 | 1.814 | 14 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 1 NPT | 1 | 33.401 | 2.209 | 11.5 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 1-1/4 NPT | 1-1/4 | 42.164 | 2.209 | 11.5 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 1-1/2 NPT | 1-1/2 | 48.26 | 2.209 | 11.5 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 2 NPT | 2 | 60.325 | 2.209 | 11.5 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 2-1/2 NPT | 2-1/2 | 73.025 | 3.175 | 8 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 3 NPT | 3 | 88.9 | 3.175 | 8 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 3-1/2 NPT | 3-1/2 | 101.6 | 3.175 | 8 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 4 NPT | 4 | 114.3 | 3.175 | 8 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 5 NPT | 5 | 141.3 | 3.175 | 8 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 6 NPT | 6 | 168.275 | 3.175 | 8 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
Equivalent Standards
Where direct equivalents exist (ISO ↔ DIN, ISO ↔ ASME), they are listed on the parent NPT Pipe Thread Fittings page.
Always confirm against the dimensions on this page, since some "equivalent" standards differ in tolerances and head geometry.
When to Specify ASME B1.20.1
ASME B1.20.1 is the inch-based reference; for metric programs choose the ISO equivalent instead.
Custom manufacturing · Made to drawing
Need a pipe & pneumatic fitting to this standard in a non-standard size?
Parts built to ASME B1 20 1 are already in the catalog, so a special is usually a variation on existing tooling rather than a new design — which is what keeps the cost down.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.
