Short answer: `HSK63-ER32` is a HSK63 machine-taper holder fitted with an ER32 collet chuck; it holds tools from 1 mm to 20 mm shank diameter. The HSK63 end goes into the spindle (1:10 hollow taper, DIN 69893, flange-contact), the ER32 end grips the tool.

Collet range is set by DIN 6499. A 12 mm end mill needs ER32 or larger; an ER32 will not close on a shank outside 1–20 mm.