balance marked 29B TSI AK

A home owner from Cailiforina says:
I have a window balance marked 29B TSI AK that looks like your 770 series, but it is 9/16" depth insted of your 1/2". Will that be a problem? From your Discussions page discussions/stamp-2900-bsi-77-2647 the photo shows the spring length to be 13,1/2". Mine is 15,1/4". Will that be a problem? My sash weight is between 19 and 20 pounds. Should I pick option 29C all so?
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Donna from SWISCO responded:
I do not foresee a problem with the the 9/16" depth versus the 1/2" depth; a 1/16" short on the depth should not effect the function, I would only be concerned if it was the other way around.

The balance stamp option is the strength of the spring, the length of the actual spring does not need to match up to the original as long as you choose the proper stamp option. To determine the proper stamp option you will need to actually remove the sash and place it on a scale.

The S770-29 with
29b stamp option will carry a window sash weight range of 12 through 18 pounds
29c stamp option will carry a window sash weight range of 18 through 23 pounds

This information is based on 2 balances per sash. Balances are designed assuming friction in the jamb weather-strip will carry a portion of the sash weight. Suggested sash weights are approximate.
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