Technical Any idea? Puller?

Found this in the bottom of a box of parts. Looks like it maybe goes to a puller? Ideas?

 

That "O" ring makes me think that it is some kind of piston, maybe out of a pneumatic tool.

 

Or from an air tool.

 

I agree with pusher-puller. The o -ring holds it in the other part of the tool

 

Gotcha! It was raising my eyebrow as I was guessing what it was...

 

You have a really long life line. Just saying.

 

Looks like the slug that slides in the back of a master cylinder. The last couple Speedway Motors masters I bought had them. They are for when your pedal doesn't have the proper length pushrod. What do I win?

 

I concur.

 

https://streetrodding.com/forums/master-cylinder/index.do?cmnt=2
Scroll down to the posts. It's a master cylinder spacer.

 

Its similar to the relief valve piston on the hydraulic system on my backhoe.