NPT Thread Dimensions — ASME B1.20.1
Basic dimensions of NPT taper pipe threads to ASME B1.20.1 in millimetres. NPT threads have a 60° thread angle and a taper of 1 in 16 on diameter (¾" per foot).
NPT is the standard thread on ASME B16.11 threaded fittings and threaded flanges. The seal is made on the thread flanks with a thread sealant; NPT and BSPT threads are not interchangeable.
NPT Thread dimensions — ASME B1.20.1 — tables
NPT basic thread dimensions
| NPSin | Threadsper inch | Pitchmm | Pipe ODmm | L1Hand-tight, mm | L2Effective thread, mm | E0Pitch dia at end, mm | E1Pitch dia at hand-tight, mm | Tap drillmm, approx. |
|---|---|---|---|---|---|---|---|---|
| 1⁄16" | 27 | 0.941 | 7.94 | 4.06 | 6.63 | 6.888 | 7.142 | 6.25 |
| ⅛" | 27 | 0.941 | 10.29 | 4.10 | 6.70 | 9.233 | 9.489 | 8.61 |
| ¼" | 18 | 1.411 | 13.72 | 5.79 | 10.21 | 12.126 | 12.487 | 11.11 |
| ⅜" | 18 | 1.411 | 17.14 | 6.10 | 10.36 | 15.545 | 15.926 | 14.68 |
| ½" | 14 | 1.814 | 21.34 | 8.13 | 13.56 | 19.264 | 19.772 | 18.26 |
| ¾" | 14 | 1.814 | 26.67 | 8.61 | 13.86 | 24.579 | 25.117 | 23.42 |
| 1" | 11.5 | 2.209 | 33.40 | 10.16 | 17.34 | 30.826 | 31.461 | 29.37 |
| 1¼" | 11.5 | 2.209 | 42.16 | 10.67 | 17.95 | 39.551 | 40.218 | 38.10 |
| 1½" | 11.5 | 2.209 | 48.26 | 10.67 | 18.38 | 45.621 | 46.287 | 44.05 |
| 2" | 11.5 | 2.209 | 60.33 | 11.07 | 19.21 | 57.633 | 58.325 | 56.36 |
| 2½" | 8 | 3.175 | 73.03 | 17.32 | 28.89 | 69.076 | 70.159 | 66.67 |
| 3" | 8 | 3.175 | 88.90 | 19.46 | 30.48 | 84.852 | 86.068 | 82.55 |
| 3½" | 8 | 3.175 | 101.60 | 20.85 | 31.75 | 97.472 | 98.776 | 95.25 |
| 4" | 8 | 3.175 | 114.30 | 21.44 | 33.02 | 110.093 | 111.433 | 107.95 |
| 5" | 8 | 3.175 | 141.30 | 23.80 | 35.72 | 136.925 | 138.412 | 134.14 |
| 6" | 8 | 3.175 | 168.28 | 24.33 | 38.42 | 163.731 | 165.252 | 161.13 |
| 8" | 8 | 3.175 | 219.07 | 27.00 | 43.50 | 214.213 | 215.901 | — |
| 10" | 8 | 3.175 | 273.05 | 30.73 | 48.90 | 267.851 | 269.772 | — |
| 12" | 8 | 3.175 | 323.85 | 34.54 | 53.98 | 318.333 | 320.492 | — |
Notes
- Millimetre values are conversions of the inch dimensions in ASME B1.20.1.
- Tap drill sizes are commonly recommended values and are not part of the standard; they depend on whether the hole is reamed.
Reference information compiled from the published standard for convenience. It does not replace the current edition of the governing standard, which takes precedence. Verify critical dimensions and properties before design, purchase or fabrication. Teshi Engineers & Sales Promoters (P) Ltd accepts no liability for errors or omissions.
Equivalent and related standards to NPT Thread Dimensions
All equivalents| Region | Standard | Relationship |
|---|---|---|
| International | ISO 7-1 / EN 10226 (BSPT) | Taper pipe threads — not interchangeable with NPT |
| China | GB/T 12716 | Chinese adoption of 60° taper pipe threads (NPT) |
| Japan | JIS B0203 | Taper pipe threads (R/Rc, BSPT form) |
Teshi Group manufactures flanges and fittings to all of these standards on request, including Chinese GB / HG / SH and European EN dimensions for export projects. Always confirm bolting, facing and thickness when substituting one standard for another.
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FAQ
NPT thread dimensions (ASME B1.20.1): common questions
How many threads per inch does a ½ inch NPT thread have?
14 threads per inch. 1⁄16" and ⅛" have 27, ¼" and ⅜" have 18, ½" and ¾" have 14, 1" to 2" have 11½, and 2½" and above have 8.
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