Tool Holder Taper Guide: BT, NT & Morse Taper (MT)

Tool holder taper specs are a core standard affecting tool accuracy and rigidity in CNC machining. The common systems are BT, NT and Morse taper (MT), differing in structure, drawbar retention and application. This guide covers BT, NT and MT holder types, the 7/24 taper ratio and key dimension symbols, to help engineers match holder and spindle for better accuracy and efficiency.

1. What a Holder Taper Is

The taper is the connection between tool and spindle; taper-face contact gives precise location, rigid clamping and fast tool changes. Three common standards:

2. The 7/24 Taper Ratio

BT and NT use a 7/24 taper — 7 units of diameter change over 24 units of length. This steep, non-self-holding taper is clamped by a drawbar, balancing locating accuracy with quick removal — the common interface for high-speed spindles. Morse taper (MT) is a smaller, self-holding taper that locks by friction and needs no drawbar.

3. BT Holder Specs (Drawbar Retention)

BT is the most common CNC standard — symmetrical, stable at high speed, retained by a drawbar. Common sizes: BT30 / BT40 / BT50 / BT60.

Drawbar thread examples (reference): BT40 → M16, BT50 → M24. Use the spec drawing for exact sizes.

Table 1 - BT drawbar taper (fig. 1)

⚠ The catalogue prints the BT45 CRKS as M20×25. A 25 mm pitch does not exist, and the rest of the series runs M12×1.75, M16×2, M24×3, M30×3.5, so this table gives M20×2.5 and records the printed value here so you can reconcile it against the catalogue you are using.

Dimensions in mm; the symbols are located on the drawing above. Values are taken from the tool holder taper page of the Mitsubishi general catalogue (p.1851), to the JIS B 6339 / MAS 403 system; for purchasing, use the model page of the maker you are actually buying from.

4. NT Holder Specs (JIS)

NT is a more traditional standard, common sizes NT30 / NT40 / NT50 / NT60. It is asymmetric and relies more on the drive key for torque, suiting traditional machines.

Table 2 - NT JIS national taper (fig. 2)

Dimensions in mm; the symbols are located on the drawing above. Values are taken from the tool holder taper page of the Mitsubishi general catalogue (p.1851), to the JIS B 6339 / MAS 403 system; for purchasing, use the model page of the maker you are actually buying from.

5. Morse Taper (MT)

Morse taper is mainly for drills, lathes and manual equipment — a self-holding taper needing no drawbar, commonly MT1–MT7. It locks by taper friction for quick mounting, but rigidity and high-speed balance are below the 7/24 system.

6. Tang vs Drawbar-Threaded Shanks

Morse shanks come in two end types:

Table 3 - Morse taper, tang shank (fig. 3)

Dimensions in mm; the symbols are located on the drawing above. Values are taken from the tool holder taper page of the Mitsubishi general catalogue (p.1851), to the JIS B 6339 / MAS 403 system; for purchasing, use the model page of the maker you are actually buying from.

Table 4 - Morse taper, drawbar-threaded shank (fig. 4)

Dimensions in mm; the symbols are located on the drawing above. Values are taken from the tool holder taper page of the Mitsubishi general catalogue (p.1851), to the JIS B 6339 / MAS 403 system; for purchasing, use the model page of the maker you are actually buying from.

7. Reading the Dimension Symbols

Spec drawings use: d1／d2／d3 (segment diameters), l1／LS (lengths), DF (flange dia), t1–t5 (structural sizes). These set spindle compatibility, tool stick-out and rigidity — confirm them together with the spindle interface when selecting.

8. CNC Selection Guide

For lathe-side holders see the Turning Tool Holder Guide and Boring Bar Guide.

This article is part of Tool Holders: The Complete Guide - One End Meets the Spindle, the Other Holds the Cutter; that guide shows how the whole topic fits together.

Published: 2026-03-25 | Last updated: 2026-07-25