Window balances

Is the metal channel, not including the nylon fittings on both ends, 29" long? If so, this is either an S380-29 or S385-29. The only difference between these two balances is the depth of the bottom nylon shoe, or heel-to-toe measurement, so compare both with your old hardware to see what matches best. Does that stamp read 28B? Check another balance to confirm. If so, for a new stamp option choose 2820.