As noted, there are a number of different size collets available from:
and there is a 3/8" collet suited for metrology (no one has reported using this for cutting — it’s a tiny thing, I’d worry about runout):
As noted, there are a number of different size collets available from:
and there is a 3/8" collet suited for metrology (no one has reported using this for cutting — it’s a tiny thing, I’d worry about runout):