A handy person from Katy Texas says:
October 26, 2014
Comes off end of a balance spring assembly. This one snapped as you can see. I'd like to order 1/2 a dozen or so since my whole house had these windows and I can use spares. Thanks. Joe
Paul from SWISCO responded:
October 28, 2014
Hey, Joe. This part is known as a shoe, and it looks like our 15-195. Check it out and let me know what you think. Just double check the width, it should be only 1-1/4". I've never seen one of these in 1-1/2".