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Hex bit shank 1/4 in (ISO 1173 C 6.3 and E 6.3): across flats 6.35 mm, across corners 7.18 mm, form C and E dimensions, 4–12.5 mm sizes + hex pocket gauge
What are the dimensions of a 1/4 inch hex bit shank (C 6.3 / E 6.3), and what size hex pocket does a bit holder need? · Standard part · basis: ISO 1173 as transcribed from the 2001 edition (forms C and E), with the 1975 edition's s1 / e table as a cross-check; one Xem-drawn hex pocket gauge plate for holder design
Also called: 1/4 hex bit dimensions, c6.3 bit dimensions, e6.3 shank dimensions, iso 1173, hex bit shank size, 1/4 inch hex shank across flats, bit holder hex pocket size, 6.35 mm hex, screwdriver bit stl, hex bit holder cad, 7/16 hex shank, 5/16 hex bit
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. Mating features
- length
- 86.6 mm
- width
- 28.7 mm
- height
- 12.0 mm
Notes
- The 1/4 in hex shank on screwdriver bits, nut drivers and quick-change chucks is ISO 1173 form C 6.3 (bit with a small ball groove, 25 mm bits) or form E 6.3 (power-tool shank with a deep groove, longer). Across flats s is 6.35 mm max and 6.29 mm min (h12) and across corners e is 7.18 mm max, 7.11 mm min. The same s / e numbers appear in the 1975 edition (6.350 / 6.292, 7.18 / 7.11), so they are stable across editions. The 1975 sample also gives 5/32 in (3.962 / 3.914), 5/16 in (7.930 / 7.872), 7/16 in (11.112 / 11.042), 5/8 in and 3/4 in (the 5/8 and 3/4 in sizes are ASME B107.4 sizes that ISO 1173:2001 does not carry).
- Letters D, A, B, C and R are as lettered in the transcribed 2001 table. The standard's figure was not available here, so what each measures (groove diameter, full-hex length, groove position, edge radius) is not stated and these columns are listed for lookup only, not drawn. One row of the transcription is flagged: the form E D value 4.7 for the 6.3 size reads smaller than the form C D 6.7, as printed. Hoffmann's data sheet for a C 6.3 bit adds only the overall length (25 mm).
- Holder design: the pocket across flats must be at least s max = 6.35 mm plus your process allowance; the pocket corners must clear e max 7.18 mm (a true hexagon of 6.35 mm has 7.33 mm across corners, which clears it). The gauge file is a plate with five through hexagon holes at the s max values for the C / E sizes, drawn at true size; it is an Xem example, not a published part.
- Not here: the ISO 1173 female hexagon forms (B, D, F, which is the holder's socket), Torx / Phillips / Pozidriv tip profiles, tolerances beyond s and e, magnetic holder geometry, and insert-bit lengths other than 25 mm.
Hex bit shank 1/4 in (ISO 1173 C 6.3 and E 6.3): across flats 6.35… size chart
| shank form | nominal (mm) | s max (mm) | s min (mm) | e max (mm) | e min (mm) | A (min) | B | D | C | R |
|---|---|---|---|---|---|---|---|---|---|---|
| C (ball-groove, 25 mm bits) | 4 | 3.96 | 3.91 | 4.48 | 4.42 | 9 | 4 | — | — | — |
| C (ball-groove, 25 mm bits) | 6.3 | 6.35 | 6.29 | 7.18 | 7.11 | 11 | 8.2 | 6.7 | — | 0.3 |
| C (ball-groove, 25 mm bits) | 8 | 7.93 | 7.87 | 8.96 | 8.90 | 13.5 | 10.2 | 8.2 | — | — |
| C (ball-groove, 25 mm bits) | 12.5 | 12.70 | 12.63 | 14.35 | 14.27 | 15.9 | 12.7 | 13.5 | — | — |
| E (deep groove, power-tool shanks) | 6.3 | 6.35 | 6.29 | 7.18 | 7.11 | 25 | ~9.5 | 4.7 | 1 (C min) | 2.4 |
| E (deep groove, power-tool shanks) | 8 | 7.93 | 7.87 | 8.96 | 8.90 | 27 | ~5.4 | 6.3 | 1.2 (C min) | 2.4 |
| E (deep groove, power-tool shanks) | 11.2 | 11.11 | 11.04 | 12.56 | 12.48 | 31.5 | ~6.7 | 8.7 | 1.2 (C min) | 2.8 |
| 1975 edition: 5/32 in | ≈4 | 3.962 | 3.914 | 4.48 | 4.42 | — | — | — | — | — |
| 1975 edition: 1/4 in | ≈6.3 | 6.350 | 6.292 | 7.18 | 7.11 | — | — | — | — | — |
| 1975 edition: 5/16 in | ≈8 | 7.930 | 7.872 | 8.96 | 8.90 | — | — | — | — | — |
| 1975 edition: 7/16 in | — | 11.112 | 11.042 | 12.56 | 12.48 | — | — | — | — | — |
| 1975 edition: 5/8 in | — | 15.875 | 15.805 | 17.94 | 17.86 | — | — | — | — | — |
| 1975 edition: 3/4 in | — | 19.050 | 18.966 | 21.53 | 21.43 | — | — | — | — | — |
Mating features
Drawn at the exact size. Open press, slide, run and socket features by your process's clearance (tolerances by process); leave designed gaps and clamp fits as drawn.
| feature | exact | mates with | fit | files |
|---|---|---|---|---|
| shank across flats s | 6.35 mm max / 6.29 mm min (1/4 in, C 6.3 and E 6.3); also 3.96, 7.93, 11.11, 12.70 mm | hex pocket in a bit holder, chuck or driver handle: at least s max plus your process allowance | slide | hex-bit-holder* |
| across corners e | 7.18 mm max / 7.11 mm min for 6.3 | pocket corners must clear e max (a true hexagon of 6.35 mm across flats has 7.33 mm across corners) | slide | hex-bit-holder* |
Where the files are
Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.
| ISO (iTeh Standards free sample) | ISO 1173:1975 screwdriver bits / hexagon drives: male hexagon s1, e for 5/32, 1/4, 5/16, 7/16, 5/8, 3/4 in | web | Standards body sample pages; dimensions are facts |
| Wikipedia (screwdriver bit) | ISO 1173:2001 shank form C and form E tables: S, D, E, A, B, C, R (transcribed) | web | CC BY-SA 4.0 (text, mirror of Wikipedia) |
| Hoffmann Group | Bit, standard, 25 mm, hexagon 1/4 in C 6.3 (maker product page and data sheet) | web | Maker product page |
Free files
★ Free files 1 parts. Generated by Xem Studio from the standard; threads are plain cylinders at major diameter. CC BY 4.0. index.json
| hex-bit-holder-gauge-4-6-3-8-11-2-12-5 | hex pocket gauge plate, 86.6 × 28.7 × 12 mm: five through hexagon holes at the ISO 1173 s max across flats 3.96, 6.35 (1/4 in), 7.93, 11.11 and 12.70 mm, smallest first, 6 mm between the holes' across-corners extents; plate size, thickness and corner radius are Xem choices; hole sizes are the shank's own maximum, so add your process allowance to them | STEP · STL |
https://xemstudio.com/mcp to Claude, ChatGPT, Cursor or any MCP client (free, no account, one minute) and it can look up exact sizes, mating fits and free STEP/STL from every chat.Plain text: sheet.txt · JSON: /api/geometry?object=hex-bit-shank-iso-1173-1-4-in
Fits with
Questions
What is the across-flats size of a 1/4 inch hex bit?
6.35 mm maximum and 6.29 mm minimum (ISO 1173 C 6.3 and E 6.3), 7.18 mm maximum across corners.
What is the difference between C 6.3 and E 6.3?
Both are 6.3 mm hexagons. C 6.3 is the bit shank with a small groove (25 mm bits), E 6.3 is the power-tool shank with a deep groove and a longer minimum length (25 against 11 mm in the A column).
What size hex pocket should a bit holder have?
At least 6.35 mm across flats (the shank's maximum) plus your process allowance for a slide fit; the gauge plate shows the true 6.35 mm size.