Window Coil parts marked with F

A home owner from USA says:
Hello,
I am attaching two pictures of sets of window coils that I need to order from you, can you please identify them for me. The only information on the coil is an F imprinted, I have no other information. We have vinyl tech windows.
Can you please advise.This is the balance coil I bought from Swissco a few years ago, please advise me.
Thank you,
Chintu
coil balance
coil balance
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Tom from SWISCO responded:
Based on your pictures, your shoe resembles our 15-177. This is compatible with our Series 152 coil spring. Look these parts over and see what you think.
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