I don't pretend to know what it came off of, but it looks to me like there were two loops/guides, and one of them is broken off; that it's likely a leather was looped over each one or was run through them, given the finish being completely worn off the survivor; and the mechanism in the middle almost has to have been designed to clamp to a strap running beneath it. Pull the piece over and rotate the offset portion to lock whatever ran through. Awfully small for anything that comes to mind. It's almost like you could slide it up and down a narrow strap and lock it in place where you wanted. Or you could have one strap end looped and attached to one end and another free end running through the other and through the locking mechanism.
