constant force tape balance identification

Thanks for posting. You're absolutely correct. We actually used to carry this exact shoe, but it was discontinued pretty recently, and the 15-177 is the substitute. Width and thickness are the most relevant dimensions for a pivot shoe; the height usually isn't all that important, hence why it shouldn't be an issue. 

 The Series 152 Coil Balances are indeed the right springs for this shoe. To know what spring weight to select, look if there's any stamp on the old coil spring, usually near the 'tongue'. If there is none, or what is there doesn't make sense to you, give me the exact weight of the window sash these coil springs support, and I can use that to work out exactly what you need. 

Coil balance systems like this are modular, and so you only need to replace what's broken. But if by chance you need new covers for the coil springs, see the 15-143, 15-144, and 15-145, each sold separately. This is a different design from your old spring covers, but works by essentially 'sandwiching' around each spring. Let me know if you have further questions. 

I'm afraid not. That could either mean "Lower," as in "lower sash," or "Left," in regards to which side of the window it sits. Either way it's not relevant to how much weight it can carry, so we will definitely need to know the weight of the sash before we can proceed.

So, the rule of thumb is to divide the sash weight by how many springs support it. For this reason we usually insist upon a precise weight, rather than an estimation; you never want to guess when it comes to balances.

That said, if your sash is 18 pounds and you use one spring per side, then you could use one 9 pound Series 152 option on each side of the window. That will add up to 18 pounds of support.

If your sash is 20 pounds, then you'll have to get creative, since we don't have a 10 pound option. In this case, you would need to use two 5 pound spring options on each side of the window. That would double the amount of cover hardware you need since you're using more springs per side.

That said, I highly recommend getting a precise sash weight before you buy anything.