Vinyl window balance

Thanks for reaching out! It looks like you have either the S380-27 with a 1" shoe or the S385-27 with a 1-3/32" shoe. To determine which series is needed for your window, look over the dimensions from the diagram below to confirm the depth of your bottom shoe. Let me know if it does not match either measurement. 

You'll need to select the 2640 stamp for a 19 to 26lb window.

Comparison of the S378, S380 and S385 balance shoes.