What is this tool thread?

I have shown these pictures to so many people and everyone suspects it's a micrometer of some kind but there's so much more tool than the small measuring piece. Also thought it looked a little like a ring land cleaner but it's not one of those either. Picked it up in a pile of engine tools. Haven't the slightest idea. Maybe a thread measurement tool? please help haha

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It's a micrometer for sure but for measuring a deep offset. A specialty instrument for sure.