Please ID this Balance assy.

A quick learner from Lake City, FL says:
From a Amsco window? U channel, appx 28" long only marking on it is "2730". See pictures for plastic end detail. The unit failed as the bottom sheeve broke at its attachement point.
Thanks
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Bob from SWISCO responded:

Hello there. This looks like either a S351-28 or S390-28 Channel Balance. The only difference between these two balances is the depth of the bottom nylon shoe, or the 'heel-to-toe' measurement. The Series 351 has a shoe that is 1" deep; the Series 390 shoe has a depth of 1-1/8". See the diagram below. Compare both with your old hardware to see what matches best. In either case, for a stamp option choose 2730. Let me know if you have further questions.

Comparison of the S351 and S390 balance shoes.
Comparison of the S351 and S390 balance shoes.

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