Sash window balance spring

A handy person from Stagecoach, nv says:
im looking for new sash balances. They are for a window that it approx 45 pounds, the ones that were installed are too weak and the spring broke. The number on it is "3240", so i would need the next "step up" for weight, these were replaced before and failed.

The channel is 9/16 wide, and 5/8 deep, the overall length (plastic end to plastic end) is 34 inches. The metal overall length is 32 15/16.

I would like 2 of these springs, and 4 of the metal retaining clips that go into the frame to allow for removal of the springs.

Please let me know if you need anymore info from me, and also if you hqve these, thank you!
Morgan
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Casey from SWISCO responded:

Hello, thanks for posting! It looks like you could have either our S380-33 or S385-33. The difference between the Series 380 and the Series 385 lies in the depth of the shoe. Take a look at the picture below for more detail. Once you have determined this dimension you should be able to select the appropriate balance. 

Comparison of the S380 and S385 balance shoes.
Comparison of the S380 and S385 balance shoes.

Because the stamp on your channel balance and the weight of your window offer disparate information in regards to the spring strength, I would recommend getting an exact weight on your window sash and referring to the chart on the product page when selecting your stamp option.

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