There are no markings other than the numbers and letters listed below:
28.5 GX CMC 11
The metal part is about 28.5 inches and the width is 1/2". Thank you

It is a standard practice in this industry to advise customers to never try to restring their balances. There is no guide or diagram for how to do this because it is absolutely not something you should attempt; these balances are under a lot of tension at all times and attempting to change out or alter the block and tackle system in any way leads to a huge risk of injury. I've seen it happen with my own eyes. Take my word for it: it's not worth whatever amount of money you're trying to save.
If your string is damaged, you need to buy a new balance. Every window shop from coast to coast will tell you the same thing. It will be easier, safer, and in the long run it will be better for your windows, too. Even if you were to successfully restring your balance, the tension would never be the same and the balances still won't function like they used to.