Jacobs Taper Dimensions

The Jacobs Taper (JT) is commonly used to secure a drill chuck to an arbor.
The dimension below should help you identify the correct arbor for your chuck
(or vice-versa!) .

Drill Chuck Taper Diagram
Dimensions in mm.

Jacobs Taper D d L Taper per mm on Diameter Incl. Angle (Approx.)
Deg. Min.
0 6.35 5.802 11.112 0.04929 2 49
1 9.754 8.469 16.669 0.07709 4 24
2 Short 13.94 12.386 19.05 0.08155 4 39
2 14.199 12.386 22.225 0.08155 4 39
33 15.85 14.237 25.4 0.0635 3 38
6 17.17 15.852 25.4 0.05191 2 58
3 20.599 18.951 30.956 0.05325 3 02
4 28.55 26.346 42.049 0.05241 2 59
5 35.89 32.422 47.625 0.05168 2 58

If your chuck dimensions don't match a taper in the above table then it's possible you have a DIN 238 taper e.g. B12 or B16.

DIN 238
Taper
D d L Taper per mm on Diameter Incl. Angle (Approx.)
Deg. Min. Sec.
B10 10.094 9.4 14.5 0.04988 2 51 27
B12 12.065 11.1 18.5 0.04988 2 51 27
B16 15.733 14.5 24 0.04995 2 51 41
B18 17.78 16.2 32 0.04995 2 51 41
B22 21.793 19.8 40.5 0.0502 2 52 31
B24 23.825 21.3 50.5 0.0502 2 52 31