Tool holders
A Morse 3 shank is 23.825 mm across its gauge line and tapers 1:19.922 (a 1.44° half angle) over a 80.962 mm plug depth; an ER32 collet clamps 1 to 20 mm. Pick a shank, Morse, 7/24 (SK, BT and CAT), HSK-A or an ER collet, and a size for its gauge Ø, its taper and how it is held, or enter a tool’s shank Ø to find the ER collets that take it.
The shank is drawn true to its taper and gauge Ø, with the tang, flange, retention knob or collet around it in proportion.
MT3 · self-holding
- Gauge Ø D
- Gauge Ø D, inch
- Small end Ø d
- Plug depth L
- Taper
- 1:19.922
- Half angle α
- 1°26'15.7"
- Included angle 2α
- 2°52'31.4"
How it’s calculated
with the taper C = 1/k for a 1:k taper. Morse tapers are each about 1:20 (self-holding, α about 1.5°); the 7/24 steep taper is C = 7/24 (α = 8°17′50″, self-releasing); HSK is 1:10 with face contact; an ER collet sits in an 8° cone. Here: α = 1°26'15.7".
| Size | Taper | Gauge Ø D | D (in) | Small end d | Plug depth L | α |
|---|---|---|---|---|---|---|
| MT0 | 1:19.212 | 9.045 | 0.3561 | 6.401 | 50.800 | 1°29'26.9" |
| MT1 | 1:20.047 | 12.065 | 0.475 | 9.373 | 53.975 | 1°25'43.5" |
| MT2 | 1:20.02 | 17.780 | 0.7 | 14.529 | 65.087 | 1°25'50.4" |
| MT3 | 1:19.922 | 23.825 | 0.938 | 19.761 | 80.962 | 1°26'15.7" |
| MT4 | 1:19.254 | 31.267 | 1.231 | 25.908 | 103.188 | 1°29'15.2" |
| MT5 | 1:19.002 | 44.399 | 1.748 | 37.465 | 131.762 | 1°30'26.2" |
| MT6 | 1:19.18 | 63.348 | 2.494 | 53.746 | 184.150 | 1°29'35.9" |
Why does a Morse taper stay in and a 7/24 taper fall out?
A Morse taper’s half angle is about 1.5°: so shallow that, pushed home, it wedges and friction holds it and drives it, and it is knocked out with a drift against its tang. The 7/24 steep taper is over 8°: it will not stick, so a drawbar pulls its retention knob in and holds it, and drive keys in the flange carry the torque. That is what lets a tool changer take it straight out. HSK is self-releasing too, but its hollow 1:10 shank is pulled in from inside until the flange face bears on the spindle as well as the taper.