Silver line series 2710, single hung balance

A home owner from Ft myers says:
Balance has 21 12 on rail. Can't seem to submit photo???
channel balance
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Paul from SWISCO responded:
It's hard to make out exactly what you have based on this photo, but it could be either our S351-22 or S390-22, based on the size of the bottom shoe. Look them over and see what you think.
A quick learner from Vero Beach says:
Hi Paul,
Those are 22inch long, correct? Mine are 28 and 1/16th long.
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Paul from SWISCO responded:

I'm afraid they don't make these in a 28-1/16" length, but they do make them in 28". You may want to double check that measurement again just to be safe. 

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