balancer weight

Good question. I see that you are inquiring about our S351-21 channel balance. Since your stamped number of "20 D" does not correspond to any of our stamped options, the best way to determine the most appropriate option would be to weigh your window sash on a scale. Once you have gotten that number, you would correspond that number to our sash weight range chart located on the product page to determine which stamped option would go best with your balance.