ISO20, ISO30, HSK 50 HSK 63????

[15mgtar]

Guys I am a newbie and I want to purchase spindle with ATC what is the difference between ISO20, ISO30, HSK 50 HSK 63 and BT30 (I want atleast can hold an 18mm endmill or larger is better)?
Thank you in advance

[yosefi83]

BT30 (and I think ISO30 as well) can take maximum 16mm. But there are special collets available that would take 18mm as well - not cheap as they are not standard.

Daniel