3130 & 31 C?

A quick learner from New York says:
Hi there,

My window broke and these came off each side. I don't know why each side has a different stamp, but I need one of each? To put my window back up
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Bob from SWISCO responded:

My guess would be that one of the balances was replaced at some point; these stamps technically are the same (3130, or 31-3, is the same in weight ratings as 31C). This balance appears to be either an S351-32 or S390-32 , depending on the depth of the bottom nylon shoe. Compare both with your old hardware to see what matches best. You can choose a stamp option of 3130. 

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