Need a balance coil

A handy person from FL. says:
I have an American Craftsman series 70. Size52x37. I need a balance coil for the left side (looking out). the coil is supported by part # 801020. Not sure what the lb. coil it takes. Will it be OK to replace just the one side? Thank you for any assistance.
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Bob from SWISCO responded:

Can you show me the entire balance assembly, including the pivot shoe it attaches to? I'd also like to know the thickness of the coil springs: I believe they will either be 1/2" or 3/8" thick. American Craftsman windows use a few different coil balance systems, so this would be the easiest way of narrowing down what you might need. 

As far as just replacing one side, you want to use equal amount of spring weight on each side of the window sash. If you happen to use different weights on each side, the window will not function correctly. To know what spring weights to select, there should be stamps on the springs. If there are none or you are uncertain, give us the exact weight of the window sash and we can work it out for you. 

A handy person from FL. says:
Thank you for your response. The thickness of the coil is 1/2". I have included more pictures of the entire balance assembly (right side looking out). Not sure if you can read the stamp on coils. Coil 1 has L #7.5 35". Coil 2 has #90 35". I will let you help me to decide exactly what I should replace and if one side of the window or both. I appreciate your assistance. David
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Bob from SWISCO responded:

Thanks for getting back to me. This appears to be a 15-228 Pivot Shoe, as well as a 15-150D Coil Support. For the coils stamped #7.5, see the S160-7 7.5 lb spring. For the spring stamped #9, see the S160-9 9 lb spring. Let me know if you have further questions. 

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