Window balance k-3440

Thanks for reaching out! It does look like you have the S390-35 given the length of your balance and the 1-1/8" shoe measurement. However to confirm, with certainty that this is the balance you need, I suggest double checking the measurement for the bottom shoe. Look over the dimensions from the diagram below. 

You'll need to select the 3440 stamp.

Comparison of the S351 and S390 balance shoes.