This is a part off a double hung tilt out window balance.

This looks like a knife-lock shoe for a tilt window channel balance. See our 15-233, or perhaps our 15-014. Compare the dimensions with an undamaged version of the shoe and see if you think either match up. It might be best to replace the balance entirely; we can help with that, but we'll need to see it out of the window, with pictures of any stamp codes and the metal channel length.