Coil spring balance

A quick learner from NJ says:
September 18, 2020
I am looking for a coil spring balance. It looks like there are 2 pivot systems in the window ( I'm not sure) . The lower has a 6 stamped on it and the upper has a 7. It is 31" from where the top of the spring seems to be connected to the bottom of the window.
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Bob from SWISCO responded:
September 23, 2020

This looks like our 15-087 Coil Balance Shoe and 15-086 Tandem Housing. This system uses our Series 180 Coil Balances. With this balance system, it's usually best to go by stamps on the coil springs themselves to confirm the spring weight, rather than the housing. If you're uncertain though, give me the exact weight of the window sash, and we can work it out for you. 
Tandem Coil Housing
Tandem Coil Housing
15-086
$1.99
Coil Housing Pivot
Coil Housing Pivot
15-087
$5.97
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