31" Ballast

Hello, thank you for posting,

It looks like you have either our Series 351, with a 15-002 bottom attachment, or Series 390, with a 15-001 bottom attachment. Take a look at the image below to determine which balance you'll need. You will need to measure an undamaged version to get an accurate measurement.

For a 31" balance, the 30A stamp should translate to a 3010 stamp option that can support a 7 to 12 lb window sash. Please compare. 

Let us know if you have any additional questions. 

Comparison of the S351 and S390 balance shoes.