As far as collet size goes, it depends on the size of milling cutters you use. ER25 goes up to 16mm (5/8" ); ER32 goes up to 20mm (say a 3/4" cutter). OTOH an ER32 collet-holder is quite a bit more bulky that ER25 and may be more difficult to mount.
Edited By OMG on 01/02/2014 15:35:09