peachtree non-tilt double-hung sash balances

A handy person from Amherst, MA says:
June 24, 2016
I have many Peachtree double-hung windows at my home, installed in 1985. The cords that operate the balances snapped in a couple of the windows, which now need to be propped open. Several pictures of a balance installed in a sash are attached.
The balance U-channel is 20-1/4" long and 5/8" square, and attached into the sash with a small screw at top and bottom. There is a plastic plug the inserts into the jamb to operate the balance.
The sash glass dimension is 30-3/4"W x 20-1/4"H and the sash weighs 15.3 lb without the wood trim.
The sash balance is stamped with the number "3648" and also has the small letters "B.S.I." stamped on it.

If you have balances that match these descriptions, I am interested in purchasing a number of them, two for current repairs, and some for future back-ups. I believe my only alternative would be to try to re-tie the string in the balance, which looks like it would be a pain.
Thanks.
User submitted photos of a window balance.
Profile picture of Paul
Paul from SWISCO responded:
June 27, 2016
Hello! Hopefully I can help. It's hard to tell based on this picture, but I believe that our Series 745 might be what you want. To be more specific, start with our S745-20 channel balance. I would also recommend the 19.25-4 stamp option; two balances with this stamp option can carry 13 through 17 pounds. What do you think?
A handy person from Amherst, MA says:
June 28, 2016
Are the S745-20 and the 19.25-4 two different balances, or versions of the same balance. I would go with your recommendation, as long as the dimensions match the ones I sent. Would it be helpful if I sent some more pictures? If so, what would you like to see more clearly? Thanks,

Dave
Profile picture of Tom
Tom from SWISCO responded:
June 28, 2016
The 19.25-4 is not a balance, it is a stamp that represents the strength of the S745-20 spring. The S745-20 has many such stamps, but based on your sash weight, the 19.25-4 is what I would recommend. I highly recommend looking over the S745-20 store page and reading the information we have there. That should help elucidate any concerns you may have.
20-1/4" Peachtree Balance
20-1/4" Peachtree Balance
S745-20
$14.87
How to Identify Replacement Channel Balances
How to Identify Replacement Channel Balances
VIDEO
WATCH >
How to replace a non-tilt channel balance
How to replace a non-tilt channel balance
GUIDE
READ >
Choosing a Non-tilt Channel Balance: What Will We Need?
Choosing a Non-tilt Channel Balance: What Will We Need?
GUIDE
READ >
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.