Channel Balance replacement

A quick learner from Michigan says:
This is a 30" long 1/2 inch balance. It looks most like your S351 except that the long "prongs" on my channel balance shoe are 1 3/16" whereas the length on your S351 is only 1".

Also, it is stamped with 3020 which is not an option you provide. The sash only weighs 7.5 lbs so I'm not sure which strength I should get. Also, this is a Nuprime Window.
User submitted photos of a window balance.
A quick learner from Michigan says:
Also, my shoe is 1 1/18 in depth, which makes me lean toward the s390 balance.
User submitted a photo of a window balance.
Profile picture of Tom
Tom from SWISCO responded:
I'm not sure what you mean by prongs. Do you mean the nylon attachments on either end? Your top one looks like our 19-002 , while the bottom one looks like our 15-001 . Like you said, that would match our Series 390 balance. Can you also confirm the length of the metal channel? If the stamp reads 3020, it should be 31" long, not 30".
A quick learner from michigan says:
Thanks. The metal part is 30" if I don't include any of the plastic ends in the measurement. Should I be measuring differently? By prongs, I meant the side that the tape measure is measuring in the 2nd picture of the top post.
Profile picture of Tom
Tom from SWISCO responded:
It is very strange for a balance with a 3020 stamp to be 30" long. I wonder if they were cut down on-site when the windows were installed. It's been known to happen, if the installer feels its necessary. Either way, if you have the S390-30 , I would recommend weighing your sash on a scale to confirm the best stamp option.
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