Anderson Narrowline Sash Spring

A handy person from Littleton MA says:
The number is either B31 or 331 followed by 1/19 1135. Only other number on it is 11600-17. Assumption is the number is 331 which aligns with one of your replacement sash springs.
User submitted photos of a window balance.
Profile picture of Paul
Paul from SWISCO responded:
Based on your stamp of "331," I recommend our 24-331 Andersen sash balance.
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