Need ID for replacement balance part number

A home owner from Seattle says:
March 29, 2017
Here are pictures of an intact balance that I need to have translated into the correct replacement part number your company uses. The sash weighs 28 lbs.
Channel measures 20" long and 9/16 wide
There are no stamps in the metal only the ink stamp in the picture.
I need four balances.
(I've included a picture of the top sash guide for reference, but do not need any of these).

Thank you,
Trevor
User submitted photos of a window balance.
Profile picture of Tom
Tom from SWISCO responded:
April 4, 2017
Sure, I think we can help. Your balance appears to match our S385-20, however your sash is a little heavier than the options we offer. We will need to make with a special 1970 option, which can carry 27-30 pounds. I'll email you a custom order link and price quote for 4 of these. You can use this order link to add the special balance to your cart as if it were any normal product.
20" Series 385 Channel Balance
20" Series 385 Channel Balance
S385-20
$9.38
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