Sash Balancer

A quick learner from Key West Florida says:
I have two different length balancers.
One is 22 inches long and has a stamp on it 21 12 BS1
One is 28 inches long and has a stamp on it 27 4 BS1

Please advise. I need 8 of the 22" and 4 of the 28"
Not sure what the stamps mean. The windows are already installed on a house I just purchased.
User submitted photos of a window balance.
Profile picture of Tom
Tom from SWISCO responded:
Hey, thanks for posting. I've narrowed this down to two possible channel balance Series: either our Series 351 or our Series 390 balances.

Now, as you can see, there is only one difference between these two Series, and that is their bottom shoe. The Series 351 uses the 15-002 while the Series 390 uses the 15-001. I can't quite tell what you have based on your pictures, though. Please carefully compare their dimensions to your own hardware and see which is a better match.
Comparison of <a href='Channel-Balance-Shoe/pd/Replacement-Sash-Support-Channel-Balance-Shoes/15-001'>15-001</a> & 15-002
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