26 5 fu cmc 2

I'm not sure what you have, unfortunately. We have dozens of different balances with that stamp. It's not a product code or anything, it just indicates the strength of the spring.

In order to figure out what Series this is, I need you to remove an undamaged version of this balance from the window and show me clear pictures of the top and bottom nylon fittings. I will also need to know the dimensions of these fittings.

Thank you for sending over the additional information. Take a look at the S350-27 channel balance with a 2650 strength option and let us know if you have any other questions.