Like I beam washers, crane washers, usually square but special applicationsThat looks like a machinable C-5 collet.
It was machines for what looks like a custom angled washer or part and can be re-cut to make whatever you desire.
Commonly called "side hill" washers.Like I beam washers, crane washers, usually square but special applications
Or conversely, it could have been made in a collet block on a mill for use in a lathe.could have been made for use in a collet block on a mill.