Depending on where you measured, might be TG75 or EOC16 (DIN 6388). A side view would be helpful, as would measured angles on the longer part of the taper (state each side, or included), and the groove diameter.
If you have a box of these things, I'd put ten cents on a bet they are TG75.
I ran into a really odd ball B& S 9 collet arbor years ago the used--- SYOZ Collets ---that
I purchased through Travers -special order. Will check my collets tomorrow; those look real close. Johnny