Need window channel balance and all other parts needed

A quick learner from Guam says:
Hi I am looking to buy window channel balances and all other hardware required to make the windows fully functional. There are 2 different size channel balances we need. One has a marking of 2820 and the other is 16B. I have attached photos of the 2820. The 16B looks identical, just shorter.
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Bob from SWISCO responded:

Thanks for writing in. Just confirm that the balances marked 2820 have a metal channel length of 29". Similarly, confirm that the balances marked 16B have a metal channel length of 17". Do not include the nylon fittings in these measurements. If these check out, then you need either our S351-17 or S390-17, as well as either our S351-29 or S390-29. The only difference between the Series 351 and Series 390 is the 'depth' of the bottom nylon shoe, so compare both with your old hardware to see what matches best. You will need stamp options of 1620 and 2820, respectively. 

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