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7:24 tool-holder tapers 30, 40, 50: CAT, BT and NMTB gauge diameter, flange diameter, length and draw bar thread (CAT40, BT40, DIN 2080)
What are the dimensions of a CAT40 and BT40 tool holder taper (gauge diameter, flange, length, pull stud thread)? · Standard part · basis: Tools-n-Gizmos' taper specification page (inch and metric tables) with CAT 40 / BT 40 values cross-checked against Industrial Monitor Direct; numbers only
Also called: cat40 dimensions, bt40 dimensions, cat40 vs bt40, 7:24 taper dimensions, cat40 taper gauge diameter, bt30 dimensions, cat50 flange diameter, bt40 pull stud thread, nmtb 40 taper, cat40 flange thickness, bt40 flange thickness, iso 7388 7:24, r8 collet dimensions
Exact dimensions. True size, with no tolerance added.
- sizes
- 9 in table
Notes
- Steep (7:24) tool-holder tapers taper 7 mm in diameter per 24 mm of length (about 16.6° included). Sizes 30, 40 and 50 share the gauge diameter 31.75, 44.45 and 69.85 mm (1.250, 1.750, 2.750 in) across the CAT (V-flange, ANSI B5.50), BT (Japanese JIS B6339) and NMTB (ANSI B5.18, DIN 2080) families; they differ in flange, length, flange thickness and the draw-bar (pull stud) thread, so CAT and BT holders are not interchangeable. Length columns are as printed (L for CAT and BT, L1 for NMTB).
- Cross-check: Industrial Monitor Direct gives CAT 40 flange thickness 19.1 mm (0.750 in = 19.05 mm here), BT 40 27.0 mm (1.063 in = 27.0 mm), pull stud thread M16 × 2 (and 5/8-11 for CAT), drive-key width 16.1 mm for both, and gauge line to pull stud face 68.4 mm for CAT 40 and 65.4 mm for BT 40 (68.25 mm in the table here: a 0.15 mm difference kept, not averaged). Drive-dog face to face 48.8 / 45.2 mm is from the same article.
- Disagreements inside the source page: the CAT 30 flange is 46.02 mm in the inch table and 50 mm in the metric table; NMTB 50 flange is 3.500 in = 88.9 mm in the inch table and 97.5 mm in the metric table; NMTB 30 / 40 lengths differ by 0.06 and 0.33 mm between the two tables; the CAT 30 draw-bar thread is 1/2-13 in one place and 1/2-16 in another. Both are shown. NMTB flange thickness is not clearly labelled in the source and is left blank. The ISO 7388-1 / ANSI / JIS numbers themselves were not read from the standards (paywalled), so check a gauge or the standard before cutting a spindle.
- No files: a holder taper is defined by a gauge diameter and 7:24 but the flange, keyway, retention-knob recess and pull-stud thread depth are not published as complete numbers in the sources read. R8 (Bridgeport) is not on this page: no dimension table was found, only forum posts and a hobby page with partial numbers (included angle 16° 51', drawbar thread 7/16-20), which are not enough to draw or tabulate.
7:24 tool-holder tapers 30, 40, 50: CAT, BT and NMTB gauge diameter… size chart
| family | size | gauge diameter D1 (mm) | flange diameter (mm) | length (mm) | flange thickness (mm) | draw bar thread |
|---|---|---|---|---|---|---|
| CAT (V-flange, ANSI B5.50 / ISO 7388-1) | 30 | 31.75 | 46.02 (metric table 50) | 47.63 | 19.05 | 1/2-13 (metric table M12) |
| CAT (V-flange, ANSI B5.50 / ISO 7388-1) | 40 | 44.45 | 63.05 | 68.25 | 19.05 | 5/8-11 (metric table M16) |
| CAT (V-flange, ANSI B5.50 / ISO 7388-1) | 50 | 69.85 | 98.41 | 101.60 | 19.05 | 1-8 (metric table M24) |
| BT (JIS B6339 / ISO 7388-1) | 30 | 31.75 | 46.00 | 48.40 | 22.00 | M12 |
| BT (JIS B6339 / ISO 7388-1) | 40 | 44.45 | 63.00 | 65.40 | 27.00 | M16 |
| BT (JIS B6339 / ISO 7388-1) | 50 | 69.85 | 100.00 | 101.80 | 38.00 | M24 |
| NMTB (ANSI B5.18 / DIN 2080) | 30 | 31.75 | 46.02 (metric table 50) | 68.33 (metric table 68.39) | — | 1/2-13 (metric table M12) |
| NMTB (ANSI B5.18 / DIN 2080) | 40 | 44.45 | 63.5 (metric table 63) | 93.73 (metric table 93.40) | — | 5/8-11 (metric table M16) |
| NMTB (ANSI B5.18 / DIN 2080) | 50 | 69.85 | 88.9 (metric table 97.5) | 127.0 | — | 1-8 (metric table M24) |
Where the files are
Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.
| Tools-n-Gizmos | Taper specifications: Morse overall length L1, socket depth L2, tang L3; CAT, BT and NMTB 7:24 gauge diameter, flange, length, draw bar thread | web | Publisher's page; dimensions are facts |
| Industrial Monitor Direct | CAT 40 vs BT 40: flange thickness, pull stud thread, drive key width, gauge line to pull stud face | web | Publisher's page; dimensions are facts |
| McMaster-Carr | CAT 40 taper end mill holders (free STEP/IGES per part, for your own design use; no redistribution) | STEP, IGES, PDF | McMaster-Carr site terms: personal design use, no redistribution verify |
| McMaster-Carr | Pull studs / retention knobs (free STEP/IGES per part, for your own design use; no redistribution) | STEP, IGES, PDF | McMaster-Carr site terms: personal design use, no redistribution verify |
Xem scan
File coming
No downloadable true-size file yet: the published figures do not fix the whole shape, and Xem never guesses a number. A measured scan is planned; request it and it moves up.
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=steep-taper-7-24-cat-bt-nmtb-30-40-50
Fits with
Questions
What is the gauge diameter of a CAT40 taper?
44.45 mm (1.750 in), the same as BT40; the CAT flange is 63.05 mm, the BT flange 63.00 mm.
What is the pull stud thread of a BT40 holder?
M16 (M16 × 2.0 in Industrial Monitor Direct); CAT 40 uses 5/8-11 in the inch table.
Are CAT40 and BT40 interchangeable?
No: the taper is the same but the flange thickness (19.05 against 27.0 mm), drive-key location and pull stud differ.