What is this?

Looking for my ice scrapper (told ya it was cold) and came across this. I can't recall what it does or why I needed it. What does
a " Telescoping gauge" without markings do? (Maybe I'll just use the case for a scrapper)

You measure the inside of something, then lock it in and use a micrometer to measure the gauge.

They are also called "snap gauges", and are very tricky to use with accurate results.