Technical information / Threads and fittings / ASME B1.1
Thread standard
ASME B1.1 · UN
Unified inch screw threads (UNC / UNF / UNEF)
The CSV uses semicolons as separators. The link carries the selected size.
| Size | nthreads/in | Ppitch | Dmajor dia. | Din | d2pitch | D1minor (int.) | d3minor (ext., UNR) | Designation |
|---|---|---|---|---|---|---|---|---|
| No. 1 | 64 | 0,397 | 1,854 | 0,0730 | 1,596 | 1,425 | 1,382 | #1-64 UNC |
| No. 2 | 56 | 0,454 | 2,184 | 0,0860 | 1,890 | 1,693 | 1,644 | #2-56 UNC |
| No. 3 | 48 | 0,529 | 2,515 | 0,0990 | 2,171 | 1,942 | 1,884 | #3-48 UNC |
| No. 4 | 40 | 0,635 | 2,845 | 0,1120 | 2,432 | 2,157 | 2,089 | #4-40 UNC |
| No. 5 | 40 | 0,635 | 3,175 | 0,1250 | 2,763 | 2,488 | 2,419 | #5-40 UNC |
| No. 6 | 32 | 0,794 | 3,505 | 0,1380 | 2,990 | 2,646 | 2,560 | #6-32 UNC |
| No. 8 | 32 | 0,794 | 4,166 | 0,1640 | 3,650 | 3,306 | 3,220 | #8-32 UNC |
| No. 10 | 24 | 1,058 | 4,826 | 0,1900 | 4,139 | 3,680 | 3,566 | #10-24 UNC |
| No. 12 | 24 | 1,058 | 5,486 | 0,2160 | 4,799 | 4,341 | 4,226 | #12-24 UNC |
| 1/4" | 20 | 1,270 | 6,350 | 0,2500 | 5,525 | 4,975 | 4,838 | 1/4-20 UNC |
| 5/16" | 18 | 1,411 | 7,938 | 0,3125 | 7,021 | 6,410 | 6,257 | 5/16-18 UNC |
| 3/8" | 16 | 1,587 | 9,525 | 0,3750 | 8,494 | 7,806 | 7,635 | 3/8-16 UNC |
| 7/16" | 14 | 1,814 | 11,113 | 0,4375 | 9,934 | 9,148 | 8,952 | 7/16-14 UNC |
| 1/2" | 13 | 1,954 | 12,700 | 0,5000 | 11,431 | 10,585 | 10,373 | 1/2-13 UNC |
| 9/16" | 12 | 2,117 | 14,287 | 0,5625 | 12,913 | 11,996 | 11,767 | 9/16-12 UNC |
| 5/8" | 11 | 2,309 | 15,875 | 0,6250 | 14,375 | 13,375 | 13,125 | 5/8-11 UNC |
| 3/4" | 10 | 2,540 | 19,050 | 0,7500 | 17,400 | 16,300 | 16,025 | 3/4-10 UNC |
| 7/8" | 9 | 2,822 | 22,225 | 0,8750 | 20,392 | 19,170 | 18,864 | 7/8-9 UNC |
| 1" | 8 | 3,175 | 25,400 | 1,0000 | 23,338 | 21,963 | 21,619 | 1-8 UNC |
| 1 1/8" | 7 | 3,629 | 28,575 | 1,1250 | 26,218 | 24,647 | 24,254 | 1 1/8-7 UNC |
| 1 1/4" | 7 | 3,629 | 31,750 | 1,2500 | 29,393 | 27,822 | 27,429 | 1 1/4-7 UNC |
| 1 3/8" | 6 | 4,233 | 34,925 | 1,3750 | 32,175 | 30,342 | 29,884 | 1 3/8-6 UNC |
| 1 1/2" | 6 | 4,233 | 38,100 | 1,5000 | 35,350 | 33,517 | 33,059 | 1 1/2-6 UNC |
| 1 3/4" | 5 | 5,080 | 44,450 | 1,7500 | 41,150 | 38,951 | 38,401 | 1 3/4-5 UNC |
| 2" | 4½ | 5,644 | 50,800 | 2,0000 | 47,134 | 44,690 | 44,079 | 2-4½ UNC |
| 2 1/4" | 4½ | 5,644 | 57,150 | 2,2500 | 53,484 | 51,040 | 50,429 | 2 1/4-4½ UNC |
| 2 1/2" | 4 | 6,350 | 63,500 | 2,5000 | 59,376 | 56,626 | 55,939 | 2 1/2-4 UNC |
| 2 3/4" | 4 | 6,350 | 69,850 | 2,7500 | 65,726 | 62,976 | 62,289 | 2 3/4-4 UNC |
| 3" | 4 | 6,350 | 76,200 | 3,0000 | 72,076 | 69,326 | 68,639 | 3-4 UNC |
| 3 1/4" | 4 | 6,350 | 82,550 | 3,2500 | 78,426 | 75,676 | 74,989 | 3 1/4-4 UNC |
| 3 1/2" | 4 | 6,350 | 88,900 | 3,5000 | 84,776 | 82,026 | 81,339 | 3 1/2-4 UNC |
| 3 3/4" | 4 | 6,350 | 95,250 | 3,7500 | 91,126 | 88,376 | 87,689 | 3 3/4-4 UNC |
| 4" | 4 | 6,350 | 101,600 | 4,0000 | 97,476 | 94,726 | 94,039 | 4-4 UNC |
Notes
- This table has been compiled by Emsal from the relevant standards. For the full text of the standard, refer to ASME.
- UNC is the coarse, UNF the fine and UNEF the extra-fine series. Valve body and bonnet bolting mostly uses UNC; the fine series are for vibration and thin walls.
- Designation: 1/2-13 UNC = 1/2" major diameter, 13 threads per inch, coarse series. A tolerance class is added: external thread 2A, internal thread 2B (general use).
- For numbered sizes, major diameter D = 0.060 + 0.013 × number (inch). The profile is the same as the ISO metric thread, but the dimensions are inch-based; do not mix with metric bolts.
- Accuracy and currency are not guaranteed; use the current edition of the standard for design and purchasing decisions. How the library is compiled →
Dimension letters
| D | Major diameter | P | Pitch (25.4 / n) |
| d2 | Pitch diameter | n | Threads per inch |
| D1 | Minor diameter (internal) | H | Fundamental triangle height |
| d3 | Minor diameter (external, UNR) | h | Basic thread height |
Joint type and P&ID symbol
UN-threaded studs and nuts bolt ASME flanges together, tightening the joint and compressing the gasket.
flangepipegasketweldbolt, nut
- Pass the stud through the holes of both flanges and fit a nut on each end.
- Tighten the nuts in a cross pattern, in several passes, to the required torque.
- On ASME B16.5 flanges, studs of 1" and below are UNC and larger sizes 8UN; material is usually ASTM A193 B7 with A194 2H nuts.
ASME flanges and valve bonnet joints require inch-threaded studs; metric EN 1092-1 flanges use M-threaded bolts.
P&ID: Flanged jointTwo short heavy lines perpendicular to the pipeline; the flange type is not shown on the diagram but given in the line list. Symbol library →
Not to scale; proportions are indicative.