BSI 29 B window balancers ....

Hello,

It's tough to be sure without seeing detailed photos of your top fitting, but the S351, with a 15-002 bottom attachment, or S390, with a 15-001 bottom attachment, would be a good place to start. Take a look at the images below to determine if one of them matches your balance. 

Also, make sure to confirm if your balance measures 30" long, not including the end fittings. If so, you'll need a 2920 spring strength option for your replacement balances. Thank you!

How to measure the length of the Series 351 channel balance.

Comparison of the S351 and S390 balance shoes.