2790 Channel balance option

A quick learner from Tomball, TX says:
I have a home approx. 14 years old with non-tilt windows and need to replace a couple channel balances. The stamp says 2790 BSI NN 30. I have not been able to find this exact match. Appreciate any assistance you can provide.

Thank you.
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Tom from SWISCO responded:
Stamps ending with "90" use an old rating system that has fallen out of use. One of our stamps may still work, but you will need to weigh your sash to determine the proper match.
A quick learner from Tomball, TX says:
Thanks. Weight is 30 lbs. So with this weight and a stamp of 2790 30 BSI NN would equate to which balance under the new rating system?

Thank you.
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Tom from SWISCO responded:
Referring to the chart on the S390-28 store page, there are two possibilities. The 2750 can carry 26 through 30 pounds, while the 2760 can carry 30 through 33 pounds. You may want to get a more exact weight to see if it leans one way or the other. If it's exactly 30 pounds down to the ounce, then I suppose either could work.
A quick learner from Tomball, TX says:
Thanks. It is 30.2 lbs so probably opt for the 2760. The metal channel was measured at 30 inches, so should go with the S390-30, correct?

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Tom from SWISCO responded:
If the metal channel is 30 inches then the S390-30 would definitely be the length you want. That's a little odd, though. A 2790 stamp implies a metal channel length of 28". I'm not sure why you have this configuration.
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