Help identifying correct part

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Home Owner from Florida

Feb 4, 2026 2:02 pm

This is stamped into my existing part:
21 12 BSM

The metal channel measures 22"

5 user uploaded images

4 Replies

Jasmine from SWISCO

Feb 4, 2026 4:03 pm

Thanks for your post! This window balance is a match for either the S351-22 or the S390-22. To determine the correct series, you'll need to measure the depth of your bottom shoe.

The stamp from your balance does not cross-reference with ours. That said, you'll need to confirm the exact sash weight to determine the stamp option for your balance. There is a chart below the product description that lists the range each stamp will support.

Comparison of the S351 and S390 balance shoes.

Home Owner from Florida

Feb 4, 2026 5:45 pm

Thank you for your help. How do I determine the exact sash weight - I'm imagining removing it, holding it while standing on a scale, and then subtracting my body weight. Would that idea work, or is there a better method?

Jasmine from SWISCO

Feb 5, 2026 8:08 am

Yes, that method will work or you can place the sash directly on the scale.