Sash window balance spring.

Hey Chris, thanks for writing in. This exact pivot shoe is unfortunately a little tricky. We've come across it a few times before, but I'm afraid there's no exact match for it. In the past we've recommended trying to use our Series 140 Coil Balance assemblies as a replacement, but there's no guarantee this will work. 

If you decide to try it out, you will need to weigh the window sash to confirm which Series 140 strength option to go with. Divide the exact sash weight in half, and this will tell you the strength of the assemblies you need on either side of the sash. For instance, if the sash weighs 10 pounds exactly, use a pair of the S140-5 5 pound assemblies, one for each side of the window.

You will also need either a new 26-398 or 26-405 pivot bar, since these are the two pivot bars compatible with this balance assembly. You'll need to ensure that at least one of the installation holes on these replacement pivot bars aligns with one of the installation holes used on the old pivot bar in the sash. I apologize we can't offer anything closer to what you have, but this is an old system that I'm pretty sure is no longer made, so this is the best we can offer. Let me know if you have any other questions about this.

By the way, I am doing a graduate degree remotely at University of Essex--hope to be back in the UK soon! 

That's correct, every balance in our inventory is weighted using pounds, not kilograms. 

And thank you, I quite enjoy it there! I can't wait to return.