Sash Window (non-tilt) Channel Balance

A quick learner from Montreal, QC says:
Hi, I'm trying to identify which channel balance I need to replace my broken one. It has "3 7 B" etched into one side, and the metal channel is 38" long. It's for a very large, non-tilt window, measuring roughly 40" in height and 43" in width. So I also need to know which weight range is appropriate. Thanks, Simone
User submitted photos of a window balance.
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Paul from SWISCO responded:
Hard to make out the depth of your bottom balance shoe. You could have either our Series 390 or Series 351 depending on its size. Look them both over and see what you think.
A quick learner from Montreal says:
Thank you - I measured the shoe width and it is 1" so I think it must be the 351 series, but now I have to figure out which stamp option (for the weight) - I'm guessing that for such a large window, it would be 3740 (for 23-30 lbs) - does that seem reasonable?
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Tom from SWISCO responded:
A stamp of 37B usually corresponds to our 3720 option. I wouldn't recommend guessing your sash weight, these are delicate systems and it's important to only get the option that matches your weight. If you want to be 100% sure, I would remove the sash from the frame and weight it on a scale.
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