I think a little clarity is needed before the OP gets confused.
Dave Halford's statement is only true if you are using metric screwed cutters (small ones at that) if you want to use imperial screwed shank or larger than 16mm metric/imperial you need the appropriate collets and holder.
DC31K was just picking fault with Daves post se above and having a bit of fun
Kwil did not realise DC31K was only joking about putting imperial screwed cutters into metric collets
Old Mart was talking specifically about screwed cutters and their specific collets
John did not realise Old Mart was just talking about screwed ones but does highlight the fact you can hold metric and imperial cutters with cylindrical shanks of various types all in an ER system
Edited By JasonB on 16/04/2021 20:30:00