# Socket set screws, inch (ASME B18.3), cup point: hex key size, cup and flat point diameter, shortest length #0 to 1

> What hex key, point diameter and minimum length does a 1/4-20 or #10-32 cup point socket set screw have?

- Category: Hardware › Fasteners
- Kind: Standard part
- Basis: ASME B18.3 hex socket set screw values as printed by AFT Fasteners, a maker sheet, fasten.it Table 5A and Torqbolt (the four agree); Travers Tool's sheet carries different point diameters and is shown as a second source; numbers only
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**Exact dimensions.** Every file is drawn at true size with no tolerance added. The holes and pins that meet another part are listed below under Mating features, with the fit each joint needs; open those by your process's clearance before making the part.

## Notes

- Inch dimensions: hex key (socket) size J nominal, cup and flat point diameter C (max / min), and the shortest nominal screw length for cup and flat points, for cone and oval points, and for half dog points. AFT's, the maker sheet's, fasten.it's and Torqbolt's tables print the same numbers except that AFT's second table prints a 0.028 in hex key for #1 where the maker sheet, Torqbolt and fasten.it print 0.035 in (0.035 is shown); each has misaligned column headers (AFT's point diameters read min / max against Torqbolt's max / min, and fasten.it labels none of them), so the column assignment here was settled by order and cross-reading, and the C max / min pair is the one Torqbolt labels 'Cup and Flat Point Diameters, max, min'. Check the standard before you use C as a design value.
- Disagreement shown, not resolved: Travers Tool's technical sheet prints a point diameter C of 0.125 / 0.114 in for 1/4, 0.156 / 0.144 for 5/16, 0.187 / 0.174 for 3/8 and 0.250 / 0.235 for 1/2 (and #4 0.056 / 0.051), smaller than the ASME B18.3 tables above (1/4: 0.132 / 0.118; 1/2: 0.291 / 0.270), and key engagement depths that also differ; it does not say which standard or revision it follows, so it is cited only as a second source here and its values are not on the table.
- Key engagement (T) is not tabulated: the sources give it in several incompatible forms (one value per size in one sheet, short and long screw values in another). The standard also gives a cone-point angle of 90° (long screws) or 118° (short screws), +/- 2°, quoted by AFT.
- Tightening torque and the shortest-length columns come from AFT's and the maker's second table (they agree); only the shortest lengths are shown. Metric set screws: set-screws-metric (M3 to M8, ISO 4026). Hex sockets, threads and cup profile: the cup is a point finish, not a published profile, so no model is drawn.
- No file: the cup / flat point diameter C is the only published number of the point, the cup recess profile and the point chamfer are not published as numbers in any source read, so a drawing would be invented. McMaster-Carr sells socket set screws with per-part STEP; linked, not copied.

## Mating features (exact size; open press / slide / run / socket by your process clearance, leave designed and clamp as drawn)

| feature | exact | mates with | fit | files |
|---|---|---|---|---|
| hex socket | nominal hex key size: #10 3/32, 1/4 1/8, 5/16 5/32, 3/8 3/16, 1/2 1/4 in | hex key of the same size | slide | all |
| thread (major diameter) | per size: #10 Ø4.826, 1/4 Ø6.350, 3/8 Ø9.525 mm | tapped hole at the tap drill, see thread-reference-tap-drills-clearance | designed | all |

## Sizes

| size | TPI UNC / UNF | hex key size J (nominal) | cup / flat point dia C max / min (in) | C max / min (mm, computed) | shortest length: cup and flat (in) | shortest length: cone and oval (in) | shortest length: half dog (in) |
|---|---|---|---|---|---|---|---|
| #0 | — / 80 | .028 in | 0.033 / 0.027 | 0.84 / 0.69 | 0.13 | 0.13 | 0.13 |
| #1 | 64 / 72 | .035 in | 0.040 / 0.033 | 1.02 / 0.84 | 0.13 | 0.19 | 0.13 |
| #2 | 56 / 64 | .035 in | 0.047 / 0.039 | 1.19 / 0.99 | 0.13 | 0.19 | 0.19 |
| #3 | 48 / 56 | .050 in | 0.054 / 0.045 | 1.37 / 1.14 | 0.19 | 0.19 | 0.19 |
| #4 | 40 / 48 | .050 in | 0.061 / 0.051 | 1.55 / 1.30 | 0.19 | 0.19 | 0.19 |
| #5 | 40 / 44 | 1/16 in | 0.067 / 0.057 | 1.70 / 1.45 | 0.19 | 0.19 | 0.19 |
| #6 | 32 / 40 | 1/16 in | 0.074 / 0.064 | 1.88 / 1.63 | 0.19 | 0.25 | 0.19 |
| #8 | 32 / 36 | 5/64 in | 0.087 / 0.076 | 2.21 / 1.93 | 0.19 | 0.25 | 0.25 |
| #10 | 24 / 32 | 3/32 in | 0.102 / 0.088 | 2.59 / 2.24 | 0.19 | 0.25 | 0.25 |
| 1/4 | 20 / 28 | 1/8 in | 0.132 / 0.118 | 3.35 / 3.00 | 0.25 | 0.31 | 0.31 |
| 5/16 | 18 / 24 | 5/32 in | 0.172 / 0.156 | 4.37 / 3.96 | 0.31 | 0.44 | 0.38 |
| 3/8 | 16 / 24 | 3/16 in | 0.212 / 0.194 | 5.38 / 4.93 | 0.38 | 0.44 | 0.44 |
| 7/16 | 14 / 20 | 7/32 in | 0.252 / 0.232 | 6.40 / 5.89 | 0.44 | 0.63 | 0.50 |
| 1/2 | 13 / 20 | 1/4 in | 0.291 / 0.270 | 7.39 / 6.86 | 0.50 | 0.63 | 0.63 |
| 5/8 | 11 / 18 | 5/16 in | 0.371 / 0.347 | 9.42 / 8.81 | 0.63 | 0.88 | 0.88 |
| 3/4 | 10 / 16 | 3/8 in | 0.450 / 0.425 | 11.43 / 10.79 | 0.75 | 1.00 | 1.00 |
| 7/8 | 9 / 14 | 1/2 in | 0.530 / 0.502 | 13.46 / 12.75 | 0.88 | 1.00 | 1.00 |
| 1 | 8 / 12 | 9/16 in | 0.609 / 0.579 | 15.47 / 14.71 | 1.00 | 1.25 | 1.25 |

## Where the files are

- AFT Fasteners: [Socket set screws dimensions and mechanical properties (ASME B18.3-2003): hex key size S, shortest length, cup / flat point diameter](https://www.aftfasteners.com/socket-set-screws-dimensions-mechanical-properties/) — web — Publisher's page; dimensions are facts
- Fastener maker sheet (hosted on a Shopify CDN, ASME B18.3-2003 alloy steel): [Socket set screws: shortest nominal length (cup / flat, cone / oval, half dog), hex key size and torque; dimension table (column headers shifted)](https://cdn2.shopify.com/s/files/1/0056/7856/3437/files/SocketsSetscr.pdf) — web — Publisher's page; dimensions are facts
- fasten.it: [ASME B18.3 Table 5A hex socket set screws, inch series (same values; headers garbled on the page)](https://fasten.it/en/norms/norm/asme_b18.3_table_5a) — web — Publisher's page; dimensions are facts
- Torqbolt: [ASME B18.3 hexagon and spline socket set screws: J, C (cup / flat point diameter max), P (min) and the other columns, #0 to 2](https://torqbolt.com/asme-b18-3-hexagon-and-spline-socket-set-screws-dimensions-standards-specifications) — web — Publisher's page; dimensions are facts
- Travers Tool: [Socket set screw technical sheet: hex socket J, shortest length B, point diameter C, key engagement T (different values from the ASME B18.3 tables for the point and the key engagement)](https://docs.travers.com/assets/pdf/597971_tech.pdf) — web — Publisher's page; dimensions are facts
- McMaster-Carr: [Socket head screws (cap, flat, set) (free STEP/IGES per part, for your own design use; no redistribution)](https://www.mcmaster.com/products/socket-head-screws/) — STEP, IGES, PDF — McMaster-Carr site terms: personal design use, no redistribution (verify at link)

## Questions

**What size allen key for a 1/4-20 set screw?**

1/8 in hex key (ASME B18.3 nominal socket size).

**What allen key for a #10-32 set screw?**

3/32 in; cup point diameter 0.102 in max / 0.088 in min; shortest cup-point length 0.19 in.

**What hex key for a 3/8-16 set screw?**

3/16 in; cup and flat point diameter 0.212 / 0.194 in; shortest cup-point length 0.38 in.

## Fits with

- [Set screws (grub screws), M3–M8 (ISO 4026)](https://xemstudio.com/objects/set-screws-metric/)
- [Socket head cap screws, inch #0 to 1-1/2 (ASME B18.3): head, hex socket, key engagement — full size table + models #0 to 1](https://xemstudio.com/objects/socket-head-cap-screws-inch-full/)
- [Flat head socket cap screws, inch (ASME B18.3, 82° countersunk) #0 to 1-1/2: head, hex socket, key engagement + models #0 to 1](https://xemstudio.com/objects/flat-head-socket-cap-screws-inch/)
- [Thread size reference: UNC / UNF and ISO metric coarse / fine — major, minor and pitch diameter, tap drill, clearance hole (close, normal, loose)](https://xemstudio.com/objects/thread-reference-tap-drills-clearance/)
- [Flexible shaft couplers, 5–10 mm bores](https://xemstudio.com/objects/shaft-couplers/)
- [Imperial machine screws: #4-40, #6-32, #8-32, 1/4-20](https://xemstudio.com/objects/imperial-machine-screws/)
- [Metric hex socket set screws by point type: flat, cone, dog and cup (ISO 4026, 4027, 4028, 4029 / DIN 913–916), M1.6–M24 incl. M10 and M12](https://xemstudio.com/objects/set-screws-metric-m10-m12-and-point-types/)
- [Hex keys (Allen keys): ISO 2936 metric 0.7–36 mm and ASME B18.3 inch .050–7/8 in: across flats, across corners, long and short arm + 31 key models](https://xemstudio.com/objects/hex-keys-iso-2936-asme-b18-3/)