Window channel balance , non tilt window

Hello, thank you for posting,

It appears you have either our Series 351, with a 15-002 bottom attachment, or Series 390, with a 15-001 bottom attachment. Take a look at the image below to determine which balance you'll need. 

You will need to measure the length of the metal channel excluding the nylon attachments and looks for stamped number on the channel that will indicate the spring strength needed. 

If you have any questions, please let me know! 

Comparison of the S351 and S390 balance shoes.