16" window balance set needed

It looks like you have either our S351-16, with a 15-002 bottom attachment, or S390-16, with a 15-001 bottom attachment. Take a look at the image below to determine which balance you'll need. You will also need a stamp option of 1550. If you have any further questions please let us know! 

Comparison of the S351 and S390 balance shoes.

If you go on the S351-16's product page, you'll see a list of number options to the right of the product image. The stamp on your channel balance is marked "15 5" which means you'll choose the option 1550. This option indicates that the balance will support a window sash between 13 and 17 pounds. I hope this helps. Let us know if you have any further questions!