Non tilt window channel balances

A contractor from Illinois says:
I have 2 windows I need channel balances for. I believe your model S390 has the correct ends and is the correct size channel. I have 34 and 22 inch long channel balancers marked 33 D and 21 D respectively. I plan to order pairs of S390-34 and S390-22. My question is: Are the 3340 and 2140 the correct options for these?

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Tom from SWISCO responded:

Hello, Mark. Yes, a stamp ending in "D" usually corresponds to our stamps that end in "40." I think you're correct on all points. You can also weigh your sash on a scale just to be 100% sure if you want.

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