I just have one good set of finger gauges and several unmarked
mandrels (grooved, wooden, etc) - just snug up the ring and mark
mandrel with pencil, sharpie, duck tape, white-out, whatever is
handy and try gauges till is matches. No mis matches and I saved a few
bob (cents), seemed obvious to me!
Andy Parker, Agate House Lapidary
Ulverston, Cumbria, England
Tel: 01229 584023