Morse taper dimensions (MT0 – MT7)
The taper behind most drill presses, lathe tailstocks, tailstock centres and a lot of milling-machine accessories. Every size has a slightly different taper — which is the one thing people get wrong.
The chart
| Taper | Large end (in) | Large end (mm) | Small end (in) | Small end (mm) | Plug depth (in) | Plug depth (mm) | Taper per foot | Half angle |
|---|---|---|---|---|---|---|---|---|
| MT0 | 0.3561 | 9.045 | 0.2520 | 6.401 | 2.00 | 50.80 | 0.6246 | 1°29′27″ |
| MT1 | 0.4750 | 12.065 | 0.3690 | 9.373 | 2⅛ | 53.98 | 0.5986 | 1°25′43″ |
| MT2 | 0.7000 | 17.780 | 0.5720 | 14.529 | 2 9/16 | 65.09 | 0.5994 | 1°25′50″ |
| MT3 | 0.9380 | 23.825 | 0.7780 | 19.761 | 3 3/16 | 80.96 | 0.6024 | 1°26′16″ |
| MT4 | 1.2310 | 31.267 | 1.0200 | 25.908 | 4 1/16 | 103.19 | 0.6233 | 1°29′15″ |
| MT4½ | 1.5000 | 38.100 | 1.2660 | 32.156 | 4.50 | 114.30 | 0.6240 | 1°29′22″ |
| MT5 | 1.7480 | 44.399 | 1.4750 | 37.465 | 5 3/16 | 131.76 | 0.6315 | 1°30′26″ |
| MT6 | 2.4940 | 63.348 | 2.1160 | 53.746 | 7.25 | 184.15 | 0.6257 | 1°29′36″ |
| MT7 | 3.2700 | 83.058 | 2.7500 | 69.850 | 10.00 | 254.00 | 0.6240 | 1°29′22″ |
How to identify the size you have
On a female socket inside a spindle you can't easily reach the small end or measure the length — and you don't need to. Measure the largest diameter across the mouth of the socket and match it to the "large end" column above. That single measurement identifies the size.
On a loose shank you can also check the small end and the length, which is worth doing if the large end has been damaged or the tool is unmarked.
MTA vs MTB — the difference that matters when you buy an arbor
Two letters that cost people real money, because the two types are not interchangeable and look almost identical in a listing photo.
| MTA | MTB | |
|---|---|---|
| Full name | Morse Taper, type A | Morse Taper, type B |
| Back end | Flat tang | Internal thread for a drawbar |
| Held in by | Taper friction; tang only resists rotation | Taper friction plus axial drawbar tension |
| Suited to | Drilling, reaming — axial load only | Milling — radial and side loads |
| Typical home | Drill presses, lathe tailstocks | Milling machine spindles |
| Watch out for | Side load can walk a tanged arbor out | Over-tightening the drawbar can damage spindle bearings |
A tang does not transmit torque, contrary to what most people assume. It exists so the arbor can be knocked out with a drift. Torque comes from the taper friction, which is exactly why a tanged arbor is not safe for milling side loads.
Which Morse size for which drill
Manufacturers group twist drills by taper size roughly as follows:
| Taper | Typical drill diameter range |
|---|---|
| MT1 | 3 – 14 mm |
| MT2 | 14 – 23 mm |
| MT3 | 23 – 32 mm |
| MT4 | 32 – 50 mm |
| MT5 | 50 – 75 mm |
Ranges as published by one tooling manufacturer; the boundaries shift between makers, so treat them as a guide for narrowing a search rather than a rule.