Window channel balance part number confusion

A quick learner from Danville, CA says:
June 9, 2015
Good afternoon,

I have two identical windows that are side by side in my bedroom. The one on the left has channel balances marked 2040. Both of those balances are broken. The window on the right has channel balances marked 21D. One of them is broken. I'd like to replace all four, and I know they both have the same weight rating, but one is an inch longer than the other.

Thanks to your excellent web site, it was pretty easy to figure out what I need, and I'm ready to order replacements (series 390), but I'm not sure what length to order, 21" or 22".

Any advice?

Thanks,

Jim
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Tom from SWISCO responded:
June 10, 2015
Both balances should be the same size on each side. Someone must have replaced these balances in the past and not known the appropriate length. Can you tell me the size of the visible glass for the sash these balances support? That will quickly allow us to determine which is better.
A quick learner from Danville, CA says:
June 10, 2015
Tom,

Thanks for the quick response. The visible glass is 22" high x 37 1/2" wide.

Jim
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Tom from SWISCO responded:
June 11, 2015
Great. In that case, I recommend the 22" long balance. That should be the better fit.
22" Series 390 Channel Balance
22" Series 390 Channel Balance
S390-22
$9.59
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