Replacement Channel Balances

A home owner from Mesa, AZ says:
I am in need of 4 replacement side load channel balances for non-tilt window sashes, also known as a block and tackle balance. for 2 vertical sliding windows. They are 9/16" which I understand you call 1/2". My 2 windows are the same size windows but on the two balances on one window, one is marked "28 4 DL Caldwell" and the other is marked "28 4 CL Caldwell". The two balances on the other window are marked "29 3 IL Caldwell".

The attached top pieces are 19-002.
The attached bottom pieces are 15-002.
So I think in need series 351.

The length of the metal bars on the one window are 28 and 15/16" not including the attached top and bottom pieces so I would think that they are 29" and model S351-29. The metal bars on the other window are 30" and I would think that the model is S351-30, even though the windows are identical. Does this seem correct to you? My concern is that the code options on you web site ( "2810, 2820, 2830, 2840, 2850 & 2860" ) do not appear on my metal channels, in fact there are no other markings on the channels. Should I order two S351-29 and two S351-30?
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Mike from SWISCO responded:
Thanks for posting on the discussion board!

If you believe you've correctly identify your replacement balances as Series 351, here are the recommend stamp options:

29" balance with "28 4" is the S351-29 with stamp option 2840

30" balance with "29 3" is the S351-30 with stamp option 2930

Let me know if you have any questions!
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