channel balance stamp option

A handy person from CO says:
August 8, 2018
The balance I am replacing is stamped 3872L. What should I replace it with??
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Tom from SWISCO responded:
August 9, 2018

Huh, that's tough... That's a spring code, but I'm not familiar with it. There's also a part number besides the 4-digit weight code that we need to figure out. Can we see the balance attachments to try to figure out which of our balances you need? Once you think you know which one you want, you'd weigh the window sash to get the right strength option on our site. 
39" Series 390 Channel Balance
39" Series 390 Channel Balance
S390-39
$13.77
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