Well, imagine my disappointment when, several years ago, I discovered that the lathe I had inherited had a spindle nose with a #4 Morse Taper, meaning that the most suitable collets for it were the rather rare and elusive 4-Cs! Over the years, I have found a draw bar and adaptor and accumulated a full run of them by 32nds as well as a couple of the big flat faced ones you grind yourself ("pot chucks"?) I just saw an old Sheldon catalog that shows the company providing collets in round,...
4-c Collets In My Old Sheldon
4-c Collets In My Old Sheldon