Balance rod

I'm not sure what you have, unfortunately. There are 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 ends as well as whatever shoe or clip is at the end of the cord. 

Lastly, you may want to verify the precise weight of the sash, down to the ounce. That stamp usually indicates a sash weight of 45 pounds but it's always good to double check just in case.\