single hung window channel balance

Thanks for your photos. Based on what I see here, you have either our Series 351 or Series 390, depending on the depth of the bottom shoe. That's the only difference between them. I recommend measuring your shoe and referring to our dimensions to confirm the best match. As the shoe on the pictured balance is broken, you need to use an undamaged version for reference.

Comparison of the S351 and S390 balance shoes.