A handy person from Las Vegas, NV says:
November 27, 2015
I'm going to order 2-17" series 395 channel balances(S395-17). I need to know how to figure out which stamp option to order. The total window size is approximately 3' high X 2' wide. That makes the sliding pane about 18" high X 20" wide. Which stamp option do I need? Is there anything on the old channel balance that would tell me?
Tom from SWISCO responded:
November 30, 2015
You can usually cross-reference the stamp printed on your metal channel to one of our options, but the most reliable way is to simply weigh your sash on a scale and refer to the chart we show on the S395-17 store page.