Need to identify Andersen sash balance

A handy person from Fairfax, VA says:
October 10, 2016
Hello,
I have Andersen windows in my house. They are in great condition, except for strings. Looking at the sash balance I see the following numbers stamped:
"5", followed (after some space) by "27" and in the corner "-1168" in smaller numbers.

It's difficult to see them on the picture, but with this description, you should be able to see it.

What replacement part should I use?

These windows were installed before I bought the house (2004), but I have no idea when. The house was built in 1972. May be they are original?

Thank you!
User submitted a photo of a window balance.
A handy person from Fairfax, VA says:
October 10, 2016
Visible glass width: 31 7/16
Visible glass height: 21 15/16
Profile picture of Casey
Casey from SWISCO responded:
October 12, 2016
Based on your stamp of 5 27, I recommend our 24-531 Andersen Sash Balance.
Andersen Sash Balance, 519, 523, 525, 527, 531
Andersen Sash Balance, 519, 523, 525, 527, 531
24-531
$54.20
How to replace an Andersen Window Balance
How to replace an Andersen Window Balance
VIDEO
WATCH >
Andersen's Narroline Sash Balances
Andersen's Narroline Sash Balances
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.