Jason asked for help identifying a spring caliper:

https://www.flickr.com/photos/122649122@N.../albums/72157677299550057

I received a similar tool from Galootaclaus (with a little help from Curt
Seeliger) back in December 2016. I posted a picture on Galoot Image Central, but
alas it is no longer accessible. The spring mechanism on mine is more
conventional, but it functions the same.

Peter McBride pointed out that it is a specialized tool used by jewelers. I have
found that it is also useful in measuring the thickness of a saw plate.

Chuck Taylor
north of Seattle USA