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

A quick learner from Minnesota says:
Do you have a replacement
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Bob from SWISCO responded:

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. 

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