Channel Balance
Greetings. You say that the metal channel, not including the fittings, is 30" long. Is that correct? If so, 33-3 would be an awfully unusual stamp to see on a balance of this length. Typically, the first two digits of a stamp code denote the height of visible glass in the window, which is 1" less than the channel balance length. So for instance, a balance stamped 33-3 would usually be 34" long, and the visible glass in the window would be 33" high.
What I'm guessing happened in your case is that whoever built the windows did not have the right-sized balances for your windows, so they cut down what they had to get them to fit. Hence why the stamp is off. What you can do is obtain the exact weight of the window sash. You can then match that exact weight with the weight ranges listed alongside each stamp option under the product description of the balance you need. In your case, it's likely going to be either the 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. See the diagram below. Compare both with your old balance to determine what you need. Let me know if you have further questions.
