Please help identify required part

A home owner from Albany says:
I have two Simonton windows that need new coil balance assemblies. One is 30x52in and the other is 27x50in.
I've identified that I need:
-4 https://www.swisco.com/Pivot-Bar-2-1_2-inch/pd/Tilt-Window-Replacement-Sash-Pivot-Bars/26-083
-4 https://www.swisco.com/coil-single/pd/Sash-Support-Coil-Balance-Accessories/15-255
but I'm not sure what spring weight I need: https://www.swisco.com/cl/Series-159-Coil-Balance. Please let me know what you recommend or if I should provide more information.
Thanks!
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Bob from SWISCO responded:
Hello there. I gather that you're converting your Simonton windows to use the 15-259 Pivot Shoe and Series 159 Coil Springs. To know what spring weights you need for the coil springs, give me the exact weight of the window sash(es) that these coil balances support. I can work out the spring weights you need from there. 
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