# Double-end studs, inch (ASME B18.31.2): clamping-type and tap-end studs 1/4 to 4 in, thread length B, body diameter, UNC / UNF

> How long is the thread on an ASME B18.31.2 stud (1/2-13, 3/4-10), and what is the body diameter?

- Category: Hardware › Fasteners
- Kind: Standard part
- Basis: fasten.it's ASME B18.31.2 Tables 2 (clamping type) and 3 (tap-end, 1.5D engagement) cross-checked with Torqbolt's inch and mm tables (same B min values, plus body diameter DS and length tolerance); numbers only
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**Exact dimensions.** True size, with no tolerance added.

## Notes

- Inches (thread size also in mm). ASME B18.31.2 covers continuous-thread and double-end studs. Clamping-type double-end studs (equal thread at both ends, a nut on each end) and tap-end studs (a long thread to screw into a tapped hole, 1.5D engagement). Columns: threads per inch for the UNC and UNF series; Bm, the nominal thread length of the tap end (fasten.it Table 3, 1.5D engagement); B min, the minimum full-thread length at each end, for stud length L ≤ 10 in, 10 < L ≤ 16 in and L > 16 in (fasten.it and Torqbolt agree on every B min value; Torqbolt also prints them in mm, e.g. 1/4 in: 19.050, 25.400, 38.100); and the minimum body diameter DS (Torqbolt) for UNC and NC-5 HF threads, UNF threads, and 8UN threads (for 1-1/8 in and up).
- Where a table gives no value (a dash) the standard lists none: e.g. no UNF series above 1-1/2 in, and no 'L ≤ 10 in' value from 3 in thread size up. The sources do not give the body diameter for the smaller sizes in the 8UN column.
- The DIN equivalents (DIN 938 / 939, metric) are on studs-din-938-din-939. Length tolerance (Torqbolt, inches): ±0.04 for stud lengths 3/4 to 2-1/2 in, ±0.08 over 2-1/2 to 4, ±0.10 over 4 to 8, ±0.12 over 8 to 16 and ±0.18 over 16.
- No files: a double-end stud with a body only slightly smaller than the thread is a plain stepped cylinder, and a plain cylinder is not worth a model. Left out: the thread-end point and chamfer (not published as numbers in the pages read).

## Sizes

| thread size (in) | mm | UNC (tpi) | UNF (tpi) | Bm tap end (in) | B min, L ≤ 10 in | B min, 10 < L ≤ 16 in | B min, L > 16 in | DS min body, UNC (in) | DS min body, UNF (in) | DS min body, 8UN (in) |
|---|---|---|---|---|---|---|---|---|---|---|
| 1/4 | 6.35 | 20 | 28 | 0.375 | 0.75 | 1 | 1.5 | .241 | .243 | — |
| 5/16 | 7.94 | 18 | 24 | 0.469 | 0.875 | 1.125 | 1.625 | .303 | .304 | — |
| 3/8 | 9.53 | 16 | 24 | 0.563 | 1 | 1.25 | 1.75 | .364 | .367 | — |
| 7/16 | 11.11 | 14 | 20 | 0.656 | 1.125 | 1.375 | 1.875 | .426 | .428 | — |
| 1/2 | 12.7 | 13 | 20 | 0.75 | 1.25 | 1.5 | 2 | .488 | .491 | — |
| 9/16 | 14.29 | 12 | 18 | 0.844 | 1.375 | 1.625 | 2.125 | .550 | .552 | — |
| 5/8 | 15.88 | 11 | 18 | 0.938 | 1.5 | 1.75 | 2.25 | .611 | .615 | — |
| 3/4 | 19.05 | 10 | 16 | 1.125 | 1.75 | 2 | 2.5 | .735 | .739 | — |
| 7/8 | 22.23 | 9 | 14 | 1.313 | 2 | 2.25 | 2.75 | .859 | .863 | — |
| 1 | 25.4 | 8 | 12 | 1.5 | 2.25 | 2.5 | 3 | .983 | .987 | — |
| 1-1/8 | 28.58 | 7 | 12 | 1.688 | 2.5 | 2.75 | 3.25 | 1.106 | 1.112 | 1.108 |
| 1-1/4 | 31.75 | 7 | 12 | 1.875 | 2.75 | 3 | 3.5 | 1.231 | 1.237 | 1.233 |
| 1-3/8 | 34.93 | 6 | 12 | 2.063 | 3 | 3.25 | 3.75 | 1.354 | 1.362 | 1.358 |
| 1-1/2 | 38.1 | 6 | 12 | 2.25 | 3.25 | 3.5 | 4 | 1.479 | 1.487 | 1.483 |
| 1-5/8 | 41.28 | — | — | 2.438 | 3.5 | 3.75 | 4.25 | — | — | 1.608 |
| 1-3/4 | 44.45 | 5 | — | 2.625 | 3.75 | 4 | 4.5 | 1.727 | — | 1.733 |
| 1-7/8 | 47.63 | — | — | 2.813 | 4 | 4.25 | 4.75 | — | — | 1.858 |
| 2 | 50.8 | 4.5 | — | 3 | 4.25 | 4.5 | 5 | 1.975 | — | 1.983 |
| 2-1/4 | 57.15 | 4.5 | — | 3.375 | 4.75 | 5 | 5.5 | 2.225 | — | 2.233 |
| 2-1/2 | 63.5 | 4 | — | 3.75 | 5.25 | 5.5 | 6 | 2.473 | — | 2.483 |
| 2-3/4 | 69.85 | 4 | — | 4.125 | 5.75 | 6 | 6.5 | 2.723 | — | 2.733 |
| 3 | 76.2 | 4 | — | 4.5 | — | 6.5 | 7 | 2.973 | — | 2.982 |
| 3-1/4 | 82.55 | 4 | — | 4.875 | — | 7 | 7.5 | 3.223 | — | 3.232 |
| 3-1/2 | 88.9 | 4 | — | 5.25 | — | 7.5 | 8 | 3.473 | — | 3.482 |
| 3-3/4 | 95.25 | 4 | — | 5.625 | — | 8 | 8.5 | 3.723 | — | 3.732 |
| 4 | 101.6 | 4 | — | 6 | — | 8.5 | 9 | 3.973 | — | 3.982 |
| length tolerance (inches), Torqbolt | — | — | — | — | ±0.04 for L 3/4 to 2-1/2; ±0.08 over 2-1/2 to 4 | ±0.10 over 4 to 8; ±0.12 over 8 to 16 | ±0.18 over 16 | — | — | — |

## Where the files are

- fasten.it: [ASME B18.31.2 continuous and double-end studs, inch series: Table 2 (clamping type) and Table 3 (tap end, 1.5D engagement): B min by stud length, Bm, UNC / UNF](https://www.fasten.it/en/norms/norm/asme_b18.31.2) — web — Reference page; numbers only
- Torqbolt: [ASME B18.31.2 clamping-type full-body studs: B min in inches and mm, minimum body diameter DS, length tolerance](https://torqbolt.com/asme-b18-31-2-clamping-type-full-body-studs-dimensions-standards-specifications) — web — Publisher's page; dimensions are facts
- Fasteners Clearinghouse: [Double-ended studs (ASME B18.31.2) listing](https://fastenersclearinghouse.com/ansi-search=ansi-b18.31.2-double-end-studs&us-length=2_1/2&Cat1=PRM249D751F1014;&Cat2=FLF2F52C3045;&Cat7=b18.31.2;) — web — Distributor listing; numbers only

## Questions

**How long is the thread on a 1/2-13 clamping stud?**

At least 1.25 in at each end for studs up to 10 in long, 1.5 in for 10 to 16 in and 2 in over 16 in (ASME B18.31.2 B min).

**What is the tap-end engagement for a 3/4-10 stud?**

Bm = 1.125 in nominal (1.5D engagement), B min 1.75 in for L up to 10 in (fasten.it Table 3).

**What is the minimum body diameter of a 1/2-13 stud?**

0.488 in (UNC); 0.491 in for 1/2-20 UNF (Torqbolt, DS).

## Fits with

- [Studs, DIN 938 and DIN 939 (double-end studs): thread length of the nut end, M5/M6 to M30, nominal lengths](https://xemstudio.com/objects/studs-din-938-din-939/)
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