16 in Window balancer with a stamp that reads "15 5 BSI"

Hello,

It looks like you have either our S351-16, with a 15-002 bottom attachment, or S390-16, with a 15-001 bottom attachment. Take a look at the image below to determine which balance you'll need. 

You'll also need a 1550 spring strength option for your replacement balances. Thank you!

Comparison of the S351 and S390 balance shoes.