Constant force window balance

Thanks for writing in. This looks like our 15-192 Pivot Shoe. This shoe is compatible with our Series 170 and Series 171 Coil Springs. The Series 171 is used if a second spring is required on each side of the sash. In your case, your old spring's stamp of 10 indicates it likely was meant to support 10 lbs of spring weight on each side of the sash, for a total of 20 lbs of support overall. I'm afraid we don't carry an individual coil spring that supports 10 lbs of weight for this balance system; however, you can simply use (1) of the S170-405 and (1) of the S171-405 on each side of the sash. Both of these coil springs are meant for 5 lbs of support apiece, so this means you'd have 10 lbs of support on either side of the window sash, equalling that needed 20 lbs of support. Let me know if you have any other questions.