Vetter window spring balance

A home owner from Wisconsin says:
It is the window spring balance system on what I think is a Vetter window.
As shown in the photos the entire piece can be removed from the window frame.
Have some windows that don't stay all the way open.
I dont think I can replace just the spring.
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Tom from SWISCO responded:

I'm afraid we won't be able to help with this project. Your friction shoe looks like our 15-104, but that's the only thing we can supply. For the complete balance, you'll have to contact the original manufacturer of the window. I apologize for the inconvenience. 

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