Window sash balances

A home owner from Chicago says:
September 19, 2017
Moved into new condo and one window wasn't working properly. After pulling it apart, the problem was only one side had a sash balance.

Stamp shows 37DS BSL PN 40

1/2 in channel

The metal seems to measure 38in though so I need to confirm what I should be buying.

Window weighs 40 lbs Forgot to mention. It is a single hung window, not sure if that makes a difference.
Channel balance
Profile picture of Tom
Tom from SWISCO responded:
September 25, 2017
Thanks for contacting us! This balance appears to match our S390-38, but with a special strength spring for your heavy sash. We can make this for you but it will need to be a custom order. Before we begin, can you tell me how many you need? Did you just need one, or did you want to replace both balances on the same sash?
A quick learner from Chicago says:
September 25, 2017
I actually would want 4 of them because I have another identical window that isn't working well right now.

Let me know about pricing.
Profile picture of Tom
Tom from SWISCO responded:
September 27, 2017
Great, thanks. I'll email you a custom order link and price quote for 4 right now.
38" Series 390 Channel Balance
38" Series 390 Channel Balance
S390-38
$13.45
How to Replace a Non-Tilt Channel Balance
How to Replace a Non-Tilt Channel Balance
VIDEO
WATCH >
How to Repair a Jammed Window
How to Repair a Jammed Window
VIDEO
WATCH >
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.