Early mill / drills had an assortment of motors and frame sizes as they had not worked out at that stage who to copy :whistling:

Standard motor sizes are 11 Ø mm, 14 Ø mm, 19 Ø mm, 24 Ø mm, 28 Ø mm, 38 Ø mm, 42 Ø mm etc

Then there are specials [ as always ] Bridgeport, that bastion of American technology, standardised on 22 Ø mm diameter with a 7mm keyway for the step speed and a step shaft of 29mm and 28mm for the Varispeed with again a 7mm keyway.

Irving, instead of a flat alloy spacer just stand it off on 4 spacers or even 4 M12 nuts like everyone else does. lol