Window balance

Hello, thank you for posting,

It appears your window uses channel balances. To further review, we will need to see additional pictures of the bottom of the channel balance to see how it attaches and the length along with the stamp number on the metal channel. From there we can get a clearer idea of the series you have. Thank you! 

Thank you for the additional pictures,

Please start by reviewing the style of the Series 765 channel balance. Compare the S765-21 channel balance with a 20-5 stamp to your original that supports a 15 to 19 lb window sash. Let us know if you have any additional questions!