Non tilt counter balance

Thanks for reaching out! It looks like you have either the S351-27 with a 1" shoe or the S390-27 with a 1-1/8" shoe. Given the stamp on your balance, the length of the channel should be 27".

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. 

You'll need to select the 2640 stamp option.

Comparison of the S351 and S390 balance shoes.