Need replacement balance spring

This looks possibly like an S395-32, just double-check the metal channel length. Look for a stamp code somewhere on the metal channel that indicates the stamp option you need. If there is none, or you are uncertain, obtain the exact weight of your window sash. You can then match that exact weight with one of the weight ranges listed alongside each stamp option on the balance product page. 

Hey Paul, thanks for getting that sash weight. While friction does play some role in balance calibration, the weight is really all you need to go off of. For a sash that weighs 21.4 lbs, a stamp option of 3130 should be what you need, as this supports a sash that weighs 16 through 23 lbs.