Cello peg hole reamer with the standard 1/25 taper.
8mm to 16mm diameter, 200mm cutting length with 3 straight cutting edges.
Comfortable wooden handle.
Workshop tip - these reamers are very sharp. Little turn and check is the key so you don't enlarge the hole too quickly.
A small piece of tape around the reamer allows you to get each peg hole the same diameter.