Old BSI part number does not match current convetions

Question

This balance is from a 1984-1985 era window. I need a replacement as one of spring's end hooks broke. It is clearly stamped with "B.S.I." and has "12 A" on it. I cannot find "A" as part of a numbering scheme.

The metal channel length is 13".
The window weighs 5lb 6oz.
Included pictures show the end nylon pieces from a couple of angles.

What part number(s) should I be trying to acquire? I think I should replace both balances while I am at it.Thank you!

Jasmine · Accepted Answer

Thanks for posting! Your channel balances appear to be either the S351-13 with a 1" shoe or the S390-13 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 should be able to use the 1210 stamp option, which can support a sash weighing 3 to 6lbs.

Comparison of the S351 and S390 balance shoes.

You should be able to use the 1210 stamp option, which can support a sash weighing 3 to 6lbs.

Comparison of the S351 and S390 balance shoes.