Morse tapers and center holes
Dimensions of tool tapers — for arbors, centers, drill shanks and tailstock quills — and of center holes for the tailstock center.
Quick answer
Morse taper MT3 (ISO 296): gauge diameter 23.825 mm, taper 1:19.922, half angle α/2 = 1°26′16″. Every Morse taper is close to 1:20, but each size has its own ratio — never exactly 1:20.
Morse and metric tapers
| Taper | D at gauge plane, mm | Taper | Half angle α/2 |
|---|---|---|---|
| Metric 4 | 4 | 1:20 | 1°25′56″ |
| Metric 6 | 6 | 1:20 | 1°25′56″ |
| Morse 0 | 9.045 | 1:19.212 | 1°29′27″ |
| Morse 1 | 12.065 | 1:20.047 | 1°25′43″ |
| Morse 2 | 17.78 | 1:20.020 | 1°25′50″ |
| Morse 3 | 23.825 | 1:19.922 | 1°26′16″ |
| Morse 4 | 31.267 | 1:19.254 | 1°29′15″ |
| Morse 5 | 44.399 | 1:19.002 | 1°30′26″ |
| Morse 6 | 63.348 | 1:19.180 | 1°29′36″ |
| Metric 80 | 80 | 1:20 | 1°25′56″ |
| Metric 100 | 100 | 1:20 | 1°25′56″ |
| Metric 120 | 120 | 1:20 | 1°25′56″ |
| Metric 160 | 160 | 1:20 | 1°25′56″ |
| Metric 200 | 200 | 1:20 | 1°25′56″ |
D is the diameter at the gauge plane — the large end on a shank. To get taper points for the program, enter D and the ratio in the taper calculator (it has Morse 0–6 buttons). A Morse taper is self-holding: it is turned to a gauge with marking blue, not just to size.
Center holes, type A (60°, no protecting chamfer)
| d (pilot), mm | D at face, mm | Depth t, min, mm |
|---|---|---|
| 0.5 * | 1.06 | 1 |
| 0.63 * | 1.32 | 1.2 |
| 0.8 | 1.7 | 1.5 |
| 1 | 2.12 | 1.9 |
| 1.25 * | 2.65 | 2.3 |
| 1.6 | 3.35 | 2.9 |
| 2 | 4.25 | 3.7 |
| 2.5 | 5.3 | 4.6 |
| 3.15 | 6.7 | 5.9 |
| 4 | 8.5 | 7.4 |
| 5 * | 10.6 | 9.2 |
| 6.3 | 13.2 | 11.5 |
| 8 * | 17 | 14.8 |
| 10 | 21.2 | 18.4 |
* — non-preferred sizes, avoid where possible. Keep depth t even with a resharpened drill, or the center will bottom out.
Which center hole for the workpiece
| d, mm | Workpiece Ø, mm |
|---|---|
| 0.5 | ≤ 4 |
| 0.8 | 4–6 |
| 1 | 6–10 |
| 1.6 | 10–16 |
| 2.5 | 16–40 |
| 4 | 40–60 |
How deep to go with the center drill for the D you need — in the center drill calculator ("with a pilot" mode, 60° cone).
Tapers: IS 1715:2002, based on ISO 296:1991 and DIN 228:1987, table 1 (lengths are unreadable in the scan and not given). Center holes: IS 2473:1975 as amended to ISO 866 (type A), and appendix A. Both texts are open at law.resource.org.