What were these used for?

[HeelSpur]

Cute little Bulldog,
but why a round hole on the 2nd one?
It has a 1/2" open end, 5/8" box end,
and the round hole is 7/16" on one side
and tapers to 1/2" on the other side.

[Lostmind]

I'm guessing a stud would fit up through the round hole. Probably came in a tool kit for
implement?

[rusty]

For when there is a spring under the nut , on the stud.
Probably a tension adjusting wrench for something...