Need BMI Window Sash

Thanks for writing in. See either our S351-21 or our S390-21. 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. You will need to choose a stamp option. Your stamp option of 2090 is from an older rating system we do not use. To know what stamp option to select, 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. Let us know if you have any other questions.