A quick learner from Orlando FL says:
September 2, 2014
Please help me select the proper balance for my window. I will need 6 of these. They are Harcar aluminum windows. the windows are double pane. The number I think stamped on them is 2990. It is a trade size 1/2 (it does measure .562) it is stamped 30 and the u channel is 30 inches long.
Tom from SWISCO responded:
September 4, 2014
Hey, thanks for posting. I've narrowed this down to two possible channel balance Series: either our Series 380 or our Series 385 balances.
Now, as you can see, there is only one difference between these two Series, and that is their bottom shoe. The Series 380 uses the 15-005 while the Series 385 uses the 15-004. I can't quite tell what you have based on your pictures, though. Please carefully compare their dimensions to your own hardware and see which is a better match.
I also recommend that you weigh your window sash, since we do not have a standard option that matches 2990.