Matching sash balance

I'm afraid this stamp code only tells us the strength of the spring calibrated inside the balance. To know its identity, we need pictures of the nylon fittings at either end of the metal channel. From there, we'll do our best to narrow down what you need. 

See our S380-27 or S385-27. 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 a stamp option of 2640.