I need to order 2 window balances

Thanks for reaching out. It looks like you have our S380-27 or S385-27 channel balance with a 2640 stamp which will support a window weighing 19 to 26lbs. To determine which series you need, you'll have to confirm the depth of your bottom shoe. Take a look at the dimensions below to confirm.

Comparison of the S378, S380 and S385 balance shoes.