Need replacement, reads 28 but measures 30"

A home owner from Wisconsin says:
June 10, 2021
Hello,

After doing a lot of research regarding a replacement for the window balance I have, I ordered the 29" balance reading 28hd. They were an inch short, and after remeasuring them, they were actually 30" but the stamp on it reads 28hb bsl (28hb, not 28hd). Not sure this makes a difference but I'm frustrated and don't understand why it measures 30 and says 28. I'm wanting to order the next size up but am worried it will also be incorrect. It looks exactly like the old with the style, just an inch short. Please help, thanks.

Marissa
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Emily from SWISCO responded:
June 15, 2021

Hi, Marissa. 

That stamp is quite weird. A stamp that begins with a '28' usually indicates a balance that is 29" long, not 30". Can you double-check that length? You can always weigh your sash to determine the appropriate spring strength option. There's a chart on the Series 751's product page that shows you which option you'll need based on the weight of your sash.

If your sash weight differs from our given weight options on the chart, we can look into a custom option. 
A home owner from Wisconsin says:
June 15, 2021
Hello Emily,

I remeasured my old one (just the metal) and it's showing 30" and just a bit, about 1/8 inch to be exact? I weighed my window sash when I ordered the first ones and it was 24lbs I believe, so those appear sufficient to hold that weight in the "HD" category. The only thing is that they were an inch shorter than the old one.

Having said that, would the ones that I bought first (29") be fine, given that they would hold the weight? Or would you recommend I buy the 30"? Not sure whether the length itself makes the most difference, the weight, or if they really have to be both. Could the 29" ones work as long as both sides are replaced to be the same and it supports the weight? Thanks for all your help.
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Paul from SWISCO responded:
June 18, 2021

Thank you so much for your patience while we looked into this.

I just have a few questions before I recommend moving up to the S751-30. The balance you received, does the balance channel overall size match besides the length? Does the balance knife shoe also match? If so, then go up to our S751-30 with a 29HD spring weight. The spring sash weight will hold between 22-28 lbs. 
30" Series 751 Channel Balance
30" Series 751 Channel Balance
S751-30
$12.05
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