How to measure a Jacobs Taper

K.N.'s picture
MSC Administrator
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.



"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.


Yes the accurate dimensions are required for each proper application, HOWEVER the length distance is also extremely important for ANY PROPER TAPER to be measured/utilized, example recent purchases on MT#3 arbors, the tapers were not long enough (IE did not bottom out when backing off the tailstock) and they could not be removed out from the tailstock without subsequent brazing a minimum 3/16" ball bearing onto the end of the tapered item so the breakfree push rod would in fact contact the bottom of them to dislodge the item when removing it for another item to be used. ANY TAPER should still protrude on the taper at least 1/4" on/at the large diameter, beyond the face of the taper socket that holds them.

Better MRO Admi...
Better MRO Administrator

Thank you for the insights.

We do recommend utilizing the above chart... And To find taper per inch:

Find the difference between major & minor diameters.

Divide the difference with the length of the taper region.

Gary Holzman

I have a 1972 Chicago14” Drill ores with the Mt2 arbor with JT33 taper chuck looking for the correct wedges to remove the chuck. The top dimension at the chuck is .500” The machine  has a slot for arbor removal but the spindle shaft does not have a slot to insert the removal tool ( key).

Better MRO Admi...
Better MRO Administrator

Hi Gary, Thanks for your inquiry. Please take a look at the below instructions. Hope this is helpful.

Jonah Held

Albrecth 0-1/8 mini chuck..jt1 is too small no idea what it needs for a arbor

Better MRO Admi...
Better MRO Administrator

Hello Jonah!

You can refer to the below chart for guidance:


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