Balance spring

See our 15-177. This pivot shoe is compatible with our Series 152 Coil Springs. I'm afraid that the stamp number on the plastic housing isn't particularly reliable. The only stamp numbers that matter would be on the coil spring itself. If you can't find any springs, or are uncertain, give us the exact weight of your window sash, and we'll work out what you need.

Thanks for providing the weight. In that case, I'd go with the S152-9 9 lb coil spring, one for each side of the sash. This equals 18 total lbs of support--being 1 lb over the sash weight shouldn't make a difference. Now this means I think it would be wise to replace the coil springs on either side of the sash--if we don't know what the spring weights are on your old coils, we don't want to risk having the weight support on each side of the sash being uneven, as this can be harm the window's function. Let me know if you have any other questions.