BSI 21A.

Hello,

Your balance is similar to the S751-22 channel balance except that it uses a locking terminal similar to the Great Lakes 15-197 shoe. We can supply these balances with the 15-197 attached but it will need to be a custom order. To get started, please write out the exact width and depth of your metal channel. I would also recommend weighing your window sash to confirm that it falls within the 10-17 lbs range supported by our 21R strength option, which we would generally recommend based on your 21A stamp. Lastly, we'll need to know the number of replacements that you need, with the minimum being two. Thank you. 

How to measure the length of the Series 751 channel balance.

Dimensions for 15-197