Help finding my counter balance

Thanks for reaching out to us. I'm having a little trouble IDing this balance. Can you confirm that the top nylon fitting on the balance you're showing us whole and undamaged? If any pieces are broken off or missing, then I would like to see an undamaged version.

Can you also tell me the depth of the bottom nylon fitting? Refer to the diagram below to see what I mean.

Comparison of the S380 and S385 balance shoes.

Thank you! After conferring with my colleagues, we've agreed that you have an old Rollyson brand window balance. This is similar in design to our Series 371, which will work as a replacement, but the major difference is that your balances should end in 1/2" increments. For example, based on your stamps they should be 33-1/2" long and 28-1/2" long; I estimate the smallest window to have a 17-1/2" long balance, but you really should double check.

Can you confirm that this is the case? If I'm right, then these will have to be custom made, since 1/2" length balances aren't stock options. I would also need to know how many of each size you need.