If you ever want to sell the internal mike set? My 3 year old at the time played in the yard with mine. They are expensive and hard to find. May even be better than a bore gauge? Normally I would boo using a caliper, but if you have the "feel" it does not matter. a good machinist can measure accurately with a yard stick! I have a new set of outside starrett mikes, 0~6", in the wood box, cheap! Vintage Bob