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You're on the right track, but not is not that.

My husband has many such tools for his profession, and I have seen them for years, I think it is a micrometer to measure the depth of a piece, cylinder, projectile

Nope, not a micrometer, but that's a good guess. It's a firearms related tool. Close, but no prize.

G'day, I was interested in the challenge, the riddle, just that Galen, thanks for the moment.