# How to measure a Jacobs Taper K.N.
How to measure a Jacobs Taper

The Jacobs Taper (AKA JT) is commonly used to secure drill press chucks to an arbor. A customer just asked us:

Question: How to measure a Jacobs Taper?

Our Answer: It can be determined by measuring the small and large diameters and then comparing it to this chart.

JT0 Dia2 = .2284 Dia1 = .250
JT1 Dia2 = .3334 Dia1 = .384
JT2 (short) Dia2 = .4876 Dia1 = .5488
JT2 Dia2 = .4876 Dia1 = .559
JT33 Dia2 = .5605 Dia1 = .624
JT6 Dia2 = .6241 Dia1 = .676
JT3 Dia2 = .7461 Dia1 = .811
JT4 Dia2 = 1.0372 Dia1 = 1.124
JT5 Dia2 = 1.3161 Dia1 = 1.413

I'll also include this chart on Morse Tapers because they are a little bit more common. Same idea here, measuring the small and large diameter and compare it to this chart.

MT0 Dia2 = .252 Dia1 = .3561
MT1 Dia2 = .369 Dia1 = .475
MT2 Dia2 = .572 Dia1 = .700
MT3 Dia2 = .778 Dia1 = .938
MT4 Dia2 = 1.020 Dia1 = 1.231
MT4.5 Dia2 = 1.266 Dia1 = 1.500
MT5 Dia2 = 1.475 Dia1 = 1.748
MT6 Dia2 = 2.116 Dia1 = 2.494
MT7 Dia2 = 2.750 Dia1 = 3.270

If you're having application issues or stuck on something challenging, let us know right here and our group of experts will help.

Anomoly

"Large" end and "small" end don't tell us where those points are along the axis, so poviding two diameters along an undefined point on the axis doesn't help define the angle.  I believe you will find that the JT-33 for example is measured along the axis at points that are one inch apart.  If my protractor is correct that would be appoximately 2 degrees.

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