Caldwell window balance

I am afraid that stamp only tells us the strength of the spring inside the balance. To know what kind or Series it is, we need to see pictures of the nylon fittings on either end. From there we should be able to help.

See our S380-26 or S385-26. The only difference between these two balances is the depth, or 'heel-to-toe' measurement, of the bottom nylon shoe, so compare both with your old hardware to see what matches up. You'll need a stamp option of 2530.