Single hung window balance

That is a peculiar stamp. It almost looks like it's missing a digit. My best guess is that it might be indicating that your sash is 38 pounds, in which case you would want to use our 2965 stamp option. Two balances with that option can carry 35 through 39 pounds.

However, I don't recommend guessing. You should weigh your sash to confirm, then check the chart on the S385-30 store page. That will let you know exactly what you need to buy without any shadow of a doubt.