# 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)?

- Category: Hardware › Machine tool tapers & collets
- Kind: 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
- Page: https://xemstudio.com/objects/steep-taper-7-24-cat-bt-nmtb-30-40-50/ · JSON: https://xemstudio.com/api/geometry?object=steep-taper-7-24-cat-bt-nmtb-30-40-50 · Plain text: https://xemstudio.com/objects/steep-taper-7-24-cat-bt-nmtb-30-40-50/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); files CC BY 4.0 or their publisher's license
- Use in every chat: add https://xemstudio.com/mcp as a connector (https://xemstudio.com/use-with-ai/)

**Exact dimensions.** True size, with no tolerance added.

## 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.

## Sizes

| 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

- 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](https://tools-n-gizmos.com/specs/Tapers.html) — 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](https://industrialmonitordirect.com/blogs/knowledgebase/cat-40-vs-bt-40-taper-key-differences-specifications) — 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)](https://www.mcmaster.com/products/cat-40) — STEP, IGES, PDF — McMaster-Carr site terms: personal design use, no redistribution (verify at link)
- McMaster-Carr: [Pull studs / retention knobs (free STEP/IGES per part, for your own design use; no redistribution)](https://www.mcmaster.com/pull-studs) — STEP, IGES, PDF — McMaster-Carr site terms: personal design use, no redistribution (verify at link)

## 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.

## Fits with

- [Morse tapers MT0–MT7 and 4-1/2: gauge diameter, small end, taper per foot, plug depth, shank length, tang length + taper plug and ring gauges](https://xemstudio.com/objects/morse-tapers-mt0-mt7/)
- [ER collets ER8, ER11, ER16, ER20, ER25, ER32, ER40, ER50: collet diameter, length, clamping range and nut thread (DIN 6499 / ISO 15488)](https://xemstudio.com/objects/er-collets-er8-er50/)