Constant force balance spring on Royal Prime window

Hello and thanks for contacting SWISCO. Because your pivot shoe looks like our 15-087, I believe you should take a look at our Series 180 balance springs; see if they match up with what you're looking for. 

Yes, based on the stamp it is a reasonable guess that the S180-8 is what you're looking for. But to be 100% sure, you may want to weigh your window sash. If it weighs 16 pounds, then the S180-8 should be perfect, since it will be supporting 8 lbs per side (equaling 16 lbs total). 

I do see the issue. Unfortunately, it looks like we sent you the wrong coil springs. We apologize for the error. We are going to send you out the correct springs along with a return label to have the incorrect ones sent back to us. 

We thank you for your continued patience with us and we are working as diligently as possible to get this matter corrected for you. 

Ah, I've come across this problem before. In fact I just had a customer earlier today asking about this. You can still  use our 15-087, but you'll need a new 26-040 pivot bar to replace your old one. I don't think this exact style shoe is made anymore (we haven't been able to track it down, anyway), but I've been told by many others who have tried it that using the 26-040 fixes the issue. Look it over and see what you think.