Thanks for the tip. Looking into the hole, it takes a flat type key. A screwdriver worked well, but wasn't ideal. Unfortunately I don't have access to a machine shop so decided to epoxy a piece of 1/4" hardened Allen wrench into the hole. Once dry, I can use a 1/4" socket.
I recently picked up this well abused L.W. Jery "The Rex" vise, and it didn't come with a check key.
I know this is a long shot, but anyone have one lying around that they'll part with?
Hole measures around 8mm (.315").
Thanks.