No idea but it appears to me that it is a two stage something or other. The pin with the hole has a lot of wear at the entrance suggesting that a lot of somethings were forced into that hole, I am guessing that the screw used to have something on it based on how large the corresponding hole in the other handle is and relative lack of wear on that side. I see it that you would put something on either the screw position or the pin with the hole position, do an operation there and then move to the other position and complete whatever it was.