28 3 Caldwell block and tackle balances

Thanks for writing in! The numbers on the balance do not always indicate the length of the metal channel. The stamp you have indicates the weight range your balances can carry to support the weight of the sash.

To determine the exact type of balance needed for your window, you'll have to examine the top and bottom nylon attachments. With that said, both of the attachments on your balance appear to be wingless. Therefore, you have either the S351-29 with a 1" shoe or the S390-29 with a 1-1/8" shoe. 

To determine which series is needed for your window, look over the dimensions from the diagram below to confirm the depth of your bottom shoe. 

You'll need to select the 2830 stamp. Feel free to reach out with any other questions.

Comparison of the S351 and S390 balance shoes.