I'll double check the heads, being they were very cheap I purchased 5 of them. One has the 35NMTB taper to fit my SPI quick change, another I installed a Morse #3. One is clearly marked Jacobs 33 but other 2 are not marked. The one with the quick change taper is made that way, no possibilty to remove it, all one piece with housing so it's possible others were made with different Jacobs tapers. I do have J6 but defiantly too big. However looking at the chart the J6 should almost want to start in a J33 being there is a chamfer on the end but don't. If I'm lucky the unmarked units are J2. I'll also check the one that has a #3 Morse, maybe it's J2, if it'd the only J2 I have I'll remove it, J33 to #3 Morse is easy to find!