ETM ER-20 Collet Chuck
 

Does anyone know what spindle threads the ETM ER-20 Collet Chuck Part#
4501928 has.

I measured them and they look to be just about 25mm. I wanted to make
a couple of holders that screw onto the spindle. But I don't know what
tap I should get. I could only find 24mm and 26mm taps.

I'm not sure if they are a standard thread. If anyone has any info on
the diameter and pitch of this thread, that would be great.

Thanks.