1 way locking slide thingy.

Another item from my uncles collection of "stuff".. I have no idea what it is. It measures about 4 inches long, has a triple ball lock mechanism inside that allows one way travel along the 3/16" rope ( I supplied that). There is no release that allows 2 way travel or direction change. It just slides one way and locks if you attempt to go the other. The bail is free to pivot.