A quick learner from Cooper City, FL says:
March 31, 2015
Hello, I was able to identify a 1/2" series 385 balance 28" lenght however my stamp says 2790 which is not on your list. Please advise on proper one to purchase?
Tom from SWISCO responded:
April 1, 2015
That is not a standard option for us, so I recommend that you weigh your window sash on a scale to get its weight. You can then cross-reference that weight to the chart we have listed under the S385-28 store page. If your sash weight is not represented by anything on our chart, let me know and we can try to custom make something for you.