To see what they look like, search Ebay for "brake drum micrometer". There are about a dozen of them on there today, and some are priced right. I have two of them left over from back when I did a lot of brake drum machining.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!