Anderson window balance

A contractor from St louis says:
April 29, 2019
Just need to make sure i order the correct replacement parts for these
Thumbnail of the uploaded file named BP31 12R 8-86 AW
Thumbnail of the uploaded file named BP31 12L 8-86 ANDERSEN Corp
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Tom from SWISCO responded:
May 1, 2019

We may be able to replace this balance, but yours is a bit peculiar. Before we go any further, can you tell me the width and thickness of the visible glass for the sash these balances support? That will help us track down the best replacement part. Thank you!
A contractor from St louis says:
May 2, 2019
Hi Tom. I tried the replacement part if 13l and 13r. Strings are too short by a good 6". Visiable glass is 34"tall by 32 1/4" wide. Etchings in corner are MC 10 XI in the circle. Theses are standard double hung windows. Do i need to try a 1331? Does the '31' indicate the string length? The guide says to use the 13 as a replacement for the 12 but strings are simply too short. And they are installed correctly. I even tried to reverse them Incase the insides were reversed when they made them. Lol.
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Tom from SWISCO responded:
May 2, 2019

The 24-1331 will not work for you. That's only for sashes with a 27-15/16" glass height, which is way too short.

Were the balances you tried our 24-13R and 24-13L? If so, I'm surprised they didn't work. These are specifically designed for sashes with a 33-15/16" glass height, which is just about what you have. I don't think we have anything else that will work better; those are the two balances designed to work in your window. Can you confirm?
Andersen Sash Balance, 13L, 12SL
Andersen Sash Balance, 13L, 12SL
24-13L
$54.20
Andersen Sash Balance, 13R, 12SR
Andersen Sash Balance, 13R, 12SR
24-13R
$54.20
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