According to Norm Dresner :

[ ... ]

I'm planning on removing the chuck this weekend and measuring the taper.
BTW, while nobody's ever found any reference to a half-size JT, there is
something called a 2-short between #2 & #3.

O.K. That could be what they used -- though Lord only knows why
they would mark that on the machine, when there is a Morse taper socket
in the spindle to allow you to change arbors for whatever size your
favorite drill chuck happens to take.

Enjoy,
DoN.

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