Anderson window balance

A home owner from Smithtown says:
September 9, 2017
The right side balance has the numbers 11600-17 just above the Anderson logo and the number 627 3 stamped on the flange where the unit was staples to the top jamb. The left side has the numbers 11600-17 below the Anderson logo and the numbers 531 one side of the staple and 598 on the other side. Which replacement part do I need? Is there a left and right?
Andersen Balance
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Paul from SWISCO responded:
September 14, 2017
The two Andersen balances you have are our 24-637 for the 627 and 24-531 for the 531. Why there are two different balance weights for your window, we aren't sure. It might be that the window was repaired at one time and the serviceman only had these sizes. Let me know the visible glass size (width by height) for the top and bottom sash. I might be able to figure out which one is correct.
A home owner from Smithtown says:
September 14, 2017
I had the windows installed new around 1989 and no repairs were done in that time. The installation of the balances looks original (no tool marks or screw holes and only the holes from the mounting staple) Maybe changes during manufacturing, who knows.
The glass size is 20.5 wide x 22 high.
The wood sash size is 24 wide by 25 high.
Upper and lower are the same size.
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Paul from SWISCO responded:
September 15, 2017
I think it would be best to go with two of our 24-637 Andersen sash balances.
Andersen Sash Balance, 623, 627, 631, 637
Andersen Sash Balance, 623, 627, 631, 637
24-637
$54.20
Andersen Sash Balance, 519, 523, 525, 527, 531
Andersen Sash Balance, 519, 523, 525, 527, 531
24-531
$54.20
How to replace an Andersen Window Balance
How to replace an Andersen Window Balance
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