Sash balance size

First off, those stamp options aren't balance sizes. They denote the strength of the balance, or rather the weight range that the balance is calibrated to support. A stamp option of 2330 supports a window sash in the weight range of 15 through 18 lbs. A stamp option of 2375 is for a sash that weighs 37 through 40 lbs. That's a huge difference, and while no stamp options are really interchangeable to begin with, this would certainly be no exception.