Windows replacement b

Thanks for reaching out! It looks like the length of the channel is 21" but you'll need to double check this to be sure. If that is correct, you'll need either the S351-21 or the S390-21 to replace your existing assembly.

Comparison of the S351 and S390 balance shoes.

To select the stamp for the balance, you'll need to look on the back of the metal channel for the stamp/marking. If your balance doesn't have one or it doesn't match ours, you'll need to confirm the exact weight of the sash. 

There is a chart below the product description that lists the weight range each stamp option can support. It is only both balance pages.