UNIQUE 27-D-40 Channel Balance Questions

A home owner from Ocala, Florida says:
I have what I believe is a Series 770 which measures 28" long. The only stamp on it is UNIQUE 27-D-40. Should I choose option 28D when ordering? The window weighs 25 pounds.
Also, is it necessary to replace the pivot lock shoes? They appear to be OK, and I couldn't find one that looks like mine. Please take a look at the pics and help me order the right stuff. Thanks!
user submitted photo of channel balance and pivot shoe
Profile picture of Donna
Donna from SWISCO responded:
Hello,

If pivot shoe is in working order, there is no need to replace.

28" Series 770 with 27D stamp will carry a window sash weight range of 23 through 28 pounds. This will work well for a 25 pound sash.

This information is based on 2 balances per sash. Balances are designed assuming friction in the jamb weather-strip will carry a portion of the sash weight. Suggested sash weights are approximate.
Reply to Thread
Use this form to ask a follow-up question or to share your experience regarding this subject.
(your email address will be kept private and is only used to inform you when a response has been made)
Current wait time is 4-7 business days
We promise that one of our experts will personally get back to you as soon as they are able. Thank you very much for your patience and understanding. If your inquiry is time-sensitive, please feel free to reach us at 856-317-6263 or at help@swisco.com.