I picked up this Federal Products dial indicator test gauge. Paid more then display piece price , but I can't get the dial to work.
It's for Continental Motors corporation , reads 0-15 + -  Has 2 1/4" opening range.
I'm guessing to check connecting rods or mains?

When I push in on the center button on the base , I can hear movement inside , but dial doesn't move.
Probably broken , but I might be stupid and missing some thing.

The gauge ring has serrations with a lock , but doesn't move. The piece on back off base adjusts with wrench

Just another shelf piece?

There is companies that repair that type tool. I watch a lot of machine shop type of videos and the machinists send all types of measuring tools out to be rebuilt. Most of them can be repaired even if they are old.

EvilDr235

I would guess that it is a specialized bore gauge designed for a single use in a factory to check the roundness of bored holes in a production environment.

I remember seeing engine building articles in all the popular car magazines with engine builders using this tool. Magazines like Hot Rod, Popular Hot Rodding, Rod Action and Street Rodder  and other magazine of this type. Most big time drag racers used them in the pits when doing a quick rebuild between rounds.

EvilDr235

Could be for checking out of round con-rods.   The small size, could also be for checking cylinder taper, 1930s and earlier.   Looks like a real quality tool.  More factory than repair shop.