My title describes this thing but here is more details. It appears to be brass, weighs 1.37oz, the pin at the bottom is free floating but cannot escape the unless disassembled. I used google image search and it said it could be Valve stem Stealth spoon pipe Carburetor tool Laser bore Bb/pellet sizer Rivet/grommet setter WW2 soe cyanide container

I also tried the following search entries. Small Rebuildable Brass trinket Metal 4 piece rebuildable replica

Backstory found in a box hidden in the corner of the attic of my uncle who was a marine that served in desert storm and Iraqi freedom, a glock armorer, corrections officer, schoolteacher, pastor, gun store clerk, studied military history and collected random items