Balance with stamp I am unable to identify

A quick learner from Vancouver WA says:
September 21, 2016
Hi there,

I have a window balance that is stamped 21 S B.S.I. I believe it coordinated with the 351 series. Can you please help me confirm?

Thank you,
Amber
User submitted image of their window hardware.
Profile picture of Paul
Paul from SWISCO responded:
September 26, 2016
Hello, Amber. As long the bottom balance shoe has a depth of 1", then our S351-21 channel balance would be a good match. I haven't seen that kind of stamp in a long time. It's likely a very old balance. I believe 21S S might stand for a very strong spring, but I'm not sure. I recommend weighing your sash on a scale and referring to the chart we h ave on the S351-21 store page.
A quick learner from Vancouver Wa says:
September 26, 2016
Thanks for your help! Sometimes I have a hard time believing 1990 is a long time ago, but it is. My sash is 14 pounds, so it looks like the 2030 version is the one I need. The boot depth is an inch, so thank you for helping match up the right product.
Profile picture of Paul
Paul from SWISCO responded:
September 28, 2016
I agree with everything stated, including the sense that 1990 was only yesterday. Oh well, that's how it goes. Let me know if we can be of any more help!
21" Series 351 Channel Balance
21" Series 351 Channel Balance
S351-21
$9.59
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.