Is This Series 390?

A quick learner from Newton NJ says:
June 30, 2021
Not sure if it's the 390. Aluminum sash windows circa 1990? Sash measures about 38x38. As seen in photo 3740 stamped on balance. Metal part of balance measures 38" long.

None of the 4 windows have top guides installed. Looking down the track the extrusion appears continuous. I think I saw a black beveled top in another apt. Would like to repair balances on two windows. Would rather order all parts at once.

Thanks,
Glenn
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Bob from SWISCO responded:
July 6, 2021

Hi Glenn. The S390-38 certainly seems possible. Another possibility is the S351-28. The only difference between these two balances is the depth of the bottom nylon shoe, or what we call the 'heel-to-toe' measurement, so compare both with your old hardware to see what matches best. The image below illustrates the difference. For a new stamp option choose 3740. If you need new Top Sash Guides as well, removing the sash for a closer view would be a great help. 

Comparison of the S351 and S390 balance shoes.
Comparison of the S351 and S390 balance shoes.
38" Series 390 Channel Balance
38" Series 390 Channel Balance
S390-38
$13.45
38" Series 351 Channel Balance
38" Series 351 Channel Balance
S351-38
$13.45
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