Tractor part?

[hlayers7]

some of the land I detected was riddled with car parts. Most of those I tossed but I found this part interesting. It looks like maybe some sort of tractor part? Maybe just an old square washer?

 

[Tony in SC]

Not a tractor part. Maybe a cap for a square tube on a post or plow?

 

[Icewing]

This is wild speculation, but it looks as if it could have slid down a bolt and capped a square nut, but on what or if that's even close is open for debate.

 

[capsmith]

Locking nut washer for maybe a disk.

 

[4x4x4]

....The radius on one side has me stumped .
How about a good cleaning and search for a makers mark?