Looking for a channel balance

Thanks for writing in. This looks like either a S351-28 or S390-28. The only difference between these two balances is the 'depth' of the bottom nylon shoe, so compare both with your old hardware to see what matches best. Your stamp code of 2790 is from an older rating system we no longer use. The best thing to do is to weigh your window sash. You can then match that exact weight with one of the weight ranges listed alongside each stamp option on the product page.