Window Channel Balance

Thanks for posting. I am confident we can help, but I am afraid that stamp doesn't tell us the balance's identity. To know the identity, we need pictures of the nylon fittings or attachments on both ends of the metal channel. The identity of the fittings tells us the identity of the channel balance. 

That stamp designates the strength of the balance, which is still important to know; however, your stamp is from a rating system that we do not use. I'd like two pieces of information if possible: first, the weight of the window sash that these balances support. Placing the sash on a bathroom scale should suffice to get this. Second, could you send us a picture of the stamp? I just want to confirm there's nothing peculiar about it, which might indicate there's something special about this balance. We should be able to narrow everything down for you from there.