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 — dimension sheet Source: Xem Studio, https://xemstudio.com/objects/hex-bit-shank-iso-1173-1-4-in/ (sheet CC BY 4.0) 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 Catalog version: 2026-10-20 Overall (mm): length 86.6, width 28.7, height 12.0 - 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. 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 — — — — — Files elsewhere (not hosted by Xem Studio; license as stated by the publisher): - 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 — https://cdn.standards.iteh.ai/samples/5753/e09ec66c04eb4e148c53c7b553bb83f3/ISO-1173-1975.pdf - 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) — https://wiki.krisyotam.com/content/wikipedia_en_all_nopic_2026-03/Screwdriver_bit - Hoffmann Group: Bit, standard, 25 mm, hexagon 1/4 in C 6.3 (maker product page and data sheet) — web — Maker product page — https://hoffmann-group.com/GB/en/houk/p/01707- Free files (CC BY 4.0, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/hex-bit-shank-iso-1173-1-4-in/index.json API: https://xemstudio.com/api/geometry?object=hex-bit-shank-iso-1173-1-4-in