Which S770 option do I need for 3500 bsi lg?

A home owner from Matthews, NC says:
July 13, 2011
I need to replace four balances and they look exactly the same as the S770 series. The only thing that is writen on my original balances is 3500 bsi lg. I know i need 35" S770. I only need to figure out which one i need B,C or D. Can you please help?

Thank you,

Dino
Profile picture of Casey
Casey from SWISCO responded:
July 14, 2011
Hi Dino,
The letters indicate different balance strengths. To figure out the needed stamp option, please remove the window sash and place it on a scale to get the weight in pounds.

35" Series 770 balance with stamp option...

35B will carry a window sash weight range of 12 through and including 22 pounds

35C will carry 22 through and including 27 pounds

35D will carry 27 through and including 32 pounds

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.
35" Series 770 Balance
35" Series 770 Balance
S770-35
$13.82
How to replace a tilt-window channel balance.
How to replace a tilt-window channel balance.
VIDEO
WATCH >
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 3-4 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 (888) 991-1929 or at help@swisco.com.