Need to fix four windows all missing these balances

This looks like either an S380-33 or S385-33. The only difference between these two balances is the 'depth' of the bottom nylon shoe, or the heel-to-toe measurement, so compare both with your old hardware to see what matches best. You will need to select a stamp option. Look for a stamp code on the metal channel. If there is none, or you are uncertain, obtain the exact weight of 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.