Block and Tackle Window Balance

This appears to be either an S380-30 or S385-30. The only difference between these two balances is the depth of the bottom nylon shoe, or the 'heel-to-toe' measurement, so compare both with your old hardware to see what matches best. 

You'll then need to choose a stamp option, which indicates the strength of the balance. I'm having trouble reading your stamp, and the stamp code 2917 is not familiar to us. Please weigh the window sash that these balances support. You can then match that exact weight with one of the weight ranges listed alongside each stamp option on the respective balance's shop page. 

Yes, that's the correct stamp option to choose for that sash weight. Let me know if you have any other questions!