Threaded Joints probably represent the oldest method of joining piping systems. Like Socket Weld fittings, threaded fittings are mainly used for small pipe diameters (Small Bore Piping); generally for piping whose nominal diameter is NPS 2 or smaller.
National Pipe Thread Taper (NPT) is a U.S. standard for tapered threads used on threaded pipes and fittings. In contrast to straight threads that are found on a bolt, a taper thread will pull tight and therefore make a fluid-tight seal. In 1864, William Sellers, being the president of Franklin Institute, presented a standard for nuts, bolts and screws, which became the National Pipe Tapered (NPT) thread.[1]
British Standard Pipe (BSP) is a family of standard screw thread types that has been adopted internationally for interconnecting and sealing pipe ends by mating an external (male) with an internal (female) thread and has been adopted as a standard scale used in plumbing fittings, except in the United States where NPT is the standard used.
National Pipe Thread Taper (NPT) Chart
| Pipe size | Thread density |
Thread pitch | Approx. thread length | Approx. thread length, hand and wrench |
Pipe nominal outside diameter, OD |
Tap drill | ||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| (inch) | (inch−1) | (inch) | (mm) | (inch) | (mm) | (turns) | (inch) | (mm) | (inch) | (mm) | (inch) | (mm) |
| 1⁄16 | 27 | 0.03703704 | 0.9407 | 0.313 | 7.950 | |||||||
| 1⁄8 | 27 | 0.03703704 | 0.9407 | 3⁄8 | 9.525 | 10 | 1⁄4 | 6.350 | 0.405 | 10.287 | 0.339 | 8.6106 |
| 1⁄4 | 18 | 0.05555555 | 1.4111 | 5⁄8 | 15.875 | 11 | 3⁄8 | 9.525 | 0.540 | 13.716 | 7⁄16 | 11.113 |
| 3⁄8 | 18 | 0.05555555 | 1.4111 | 5⁄8 | 15.875 | 11 | 3⁄8 | 9.525 | 0.675 | 17.145 | 37⁄64 | 14.684 |
| 1⁄2 | 14 | 0.07142857 | 1.8143 | 3⁄4 | 19.0500 | 10 | 7⁄16 | 11.1125 | 0.840 | 21.3360 | 23⁄32 | 18.2563 |
| 3⁄4 | 14 | 0.07142857 | 1.8143 | 3⁄4 | 19.0500 | 10 | 1⁄2 | 12.7000 | 1.050 | 26.6700 | 59⁄64 | 23.4156 |
| 1 | 11 1⁄2 | 0.08695652 | 2.2087 | 7⁄8 | 22.2250 | 10 | 9⁄16 | 14.2875 | 1.315 | 33.4010 | 1 5⁄32 | 29.3688 |
| 1 1⁄4 | 11 1⁄2 | 0.08695652 | 2.2087 | 1 | 25.4000 | 11 | 9⁄16 | 14.2875 | 1.660 | 42.1640 | 1 1⁄2 | 38.1000 |
| 1 1⁄2 | 11 1⁄2 | 0.08695652 | 2.2087 | 1 | 25.4000 | 11 | 9⁄16 | 14.2875 | 1.900 | 48.2600 | 1 47⁄64 | 44.0531 |
| 2 | 11 1⁄2 | 0.08695652 | 2.2087 | 1 | 25.4000 | 11 | 5⁄8 | 15.8750 | 2.375 | 60.3250 | 2 7⁄32 | 56.3563 |
| 2 1⁄2 | 8 | 0.125 | 3.1750 | 1 1⁄2 | 38.1000 | 12 | 7⁄8 | 22.2250 | 2.875 | 73.0250 | 2 5⁄8 | 66.6750 |
| 3 | 8 | 0.125 | 3.1750 | 1 1⁄2 | 38.1000 | 12 | 1 | 25.4000 | 3.500 | 88.9000 | 3 1⁄4 | 82.5500 |
| 3 1⁄2 | 8 | 0.125 | 3.1750 | 5⁄8 | 15.8750 | 13 | 1 1⁄16 | 26.9875 | 4.000 | 101.6000 | 3 3⁄4 | 95.2500 |
| 4 | 8 | 0.125 | 3.1750 | 1 5⁄8 | 41.2750 | 13 | 1 1⁄16 | 26.9875 | 4.500 | 114.3000 | 4 1⁄4 | 107.9500 |
| 4 1⁄2 | 8 | 0.125 | 3.1750 | 5.000 | 127.0000 | 4 3⁄4 | 120.6500 | |||||
| 5 | 8 | 0.125 | 3.1750 | 1 3⁄4 | 44.4500 | 14 | 1 3⁄16 | 30.1625 | 5.563 | 141.3002 | 5 9⁄32 | 134.1438 |
| 6 | 8 | 0.125 | 3.1750 | 1 3⁄4 | 44.4500 | 14 | 1 3⁄16 | 30.1625 | 6.625 | 168.2750 | 6 11⁄32 | 161.1313 |
| 8 | 8 | 0.125 | 3.1750 | 1 7⁄8 | 47.6250 | 15 | 1 5⁄16 | 33.3375 | 8.625 | 219.0750 | ||
| 10 | 8 | 0.125 | 3.1750 | 2 | 50.8000 | 16 | 1 1⁄2 | 38.1000 | 10.750 | 273.0500 | ||
| 12 | 8 | 0.125 | 3.1750 | 2 1⁄8 | 53.9750 | 17 | 1 5⁄8 | 41.2750 | 12.750 | 323.8500 | ||
| 14 | 8 | 0.125 | 3.1750 | 14.000 | 355.6000 | |||||||
| 16 | 8 | 0.125 | 3.1750 | 16.000 | 406.4000 | |||||||
| 18 | 8 | 0.125 | 3.1750 | 18.000 | 457.2000 | |||||||
| 20 | 8 | 0.125 | 3.1750 | 20.000 | 508.0000 | |||||||
| 24 | 8 | 0.125 | 3.1750 | 24.000 | 609.6000 | |||||||
British Standard Pipe (BSP) Chart
| Nominal size |
Dash size |
Thread density |
Thread pitch |
Major diameter |
Minor diameter[3][4] |
Gauge length |
Typ. nut size |
Corresponding pipe | Tapping drill size | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| DN | OD | Thickness | BSP.PL, Rp | BSP.F, G | |||||||||||||
| (in) | (in−1) | (mm) | (in) | (mm) | (in) | (mm) | (in) | (mm) | (mm) | (mm) | (mm) | (in) | (mm) | (mm) | (mm) | ||
| 1⁄16 | −1 | 28 | 0.907 | 0.0357 | 7.723 | 0.304 | 6.561 | 0.2583 | 4±0.9 | 6.60 | 6.80 | ||||||
| 1⁄8 | −2 | 28 | 0.907 | 0.0357 | 9.728 | 0.383 | 8.565 | 0.3372 | 4±0.9 | 15 | 6 | 10.2 | 0.40 | 2 | 8.60 | 8.80 | |
| 1⁄4 | −4 | 19 | 1.337 | 0.0526 | 13.157 | 0.518 | 11.445 | 0.4506 | 6±1.3 | 19 | 8 | 13.5 | 0.53 | 2.3 | 11.50 | 11.80 | |
| 3⁄8 | −6 | 19 | 1.337 | 0.0526 | 16.662 | 0.656 | 14.950 | 0.5886 | 6.4±1.3 | 22 or 23 | 10 | 17.2 | 0.68 | 2.3 | 15.00 | 15.25 | |
| 1⁄2 | −8 | 14 | 1.814 | 0.0714 | 20.955 | 0.825 | 18.633 | 0.7336 | 8.2±1.8 | 27 | 15 | 21.3 | 0.84 | 2.6 | 18.75 | 19.00 | |
| 5⁄8 | −10 | 14 | 1.814 | 0.0714 | 22.911 | 0.902 | 20.589 | 0.8106 | 16 | 2.6 | – | 21.00 | |||||
| 3⁄4 | −12 | 14 | 1.814 | 0.0714 | 26.441 | 1.041 | 24.120 | 0.9496 | 9.5±1.8 | 32 | 20 | 26.9 | 1.06 | 2.6 | 24.25 | 24.50 | |
| 1 | −16 | 11 | 2.309 | 0.0909 | 33.249 | 1.309 | 30.292 | 1.1926 | 10.4±2.3 | 43 | 25 | 33.7 | 1.33 | 3.2 | 30.40 | 30.75 | |
| 1 1⁄4 | −20 | 11 | 2.309 | 0.0909 | 41.910 | 1.650 | 38.953 | 1.5336 | 12.7±2.3 | 53 | 32 | 42.4 | 1.67 | 3.2 | 39.00 | 39.50 | |
| 1 1⁄2 | −24 | 11 | 2.309 | 0.0909 | 47.803 | 1.882 | 44.846 | 1.7656 | 12.7±2.3 | 57 | 40 | 48.3 | 1.90 | 3.2 | 45.00 | 45.00 | |
| 2 | −32 | 11 | 2.309 | 0.0909 | 59.614 | 2.347 | 56.657 | 2.2306 | 15.9±2.3 | 70 | 50 | 60.3 | 2.37 | 3.6 | 56.75 | 57.00 | |
| 2 1⁄2 | −40 | 11 | 2.309 | 0.0909 | 75.184 | 2.960 | 72.227 | 2.8436 | 17.5±3.5 | 65 | 76.1 | 3.00 | 3.6 | ||||
| 3 | −48 | 11 | 2.309 | 0.0909 | 87.884 | 3.460 | 84.927 | 3.3436 | 20.6±3.5 | 80 | 88.9 | 3.50 | 4 | ||||
| 4 | −64 | 11 | 2.309 | 0.0909 | 113.030 | 4.450 | 110.073 | 4.3336 | 25.5±3.5 | 100 | 114.3 | 4.50 | 4.5 | ||||
| 5 | −80 | 11 | 2.309 | 0.0909 | 138.430 | 5.450 | 135.472 | 5.3335 | 28.6±3.5 | 125 | 139.7 | 5.50 | 5 | ||||
| 6 | −96 | 11 | 2.309 | 0.0909 | 163.830 | 6.450 | 160.872 | 6.3335 | 28.6±3.5 | 150 | 165.1 | 6.50 | 5 | ||||
