Window balances

Thanks for posting. I am confident we can help, but that stamp is actually not an identifier. It just tells us the strength of the balance. To know what balance you need, we go off the nylon attachments at both ends. It's a bit tough to see them clearly while the balance is still in the window, but I think this might be either an S380-34 or S385-24 Channel Balance. The difference between these two kinds of balances is the 'depth' of the bottom nylon shoe. See below. Measure your old balance's shoe depth to see what matches best. In either case, for a stamp option choose 3350.

Comparison of the S378, S380 and S385 balance shoes.