looking at replacing my sem servo motor with something like this

http://www.ebay.co.uk/itm/3KW-WATER-...item2a52124388

as my machine has an ATC I need to get a pulley attached to the end of the spindle.

the plan would be to mod and existing pulley rather than make a new one, so question is where do I find thread details of an ER20?

many thanks