Need sash balances

A quick learner from Florida says:
We suspect that these original balances were too weak to work properly. All the houses in our development used the same identical window, except ours.
We have double pane glass, but we suspect the contractor used the same balances as for the lighter windows.
That's why I included the actual weight of the window for your calculation.
They are
17" long (metal only)
There are nylon (?) guides on both ends.
The window weigh 33.5 lbs.
There are "wings" on both guides (see photos)

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Casey from SWISCO responded:

Hello,

With this combination of attachments, you could have the S380 or S385 channel balance. You’ll need to measure as shown below to determine the correct replacement. The Series 380 has a 1" bottom attachment, and the Series 385 has a 1-3/32" attachment. We also carry the smaller 15-029 bottom fitting with a depth of 7/8".

Once we determine the correct series and the number of balances that you need, we'll be able to determine the strength option needed to support your 33-1/2 pound sash. Thank you!

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

Dimensions for 15-029
Dimensions for 15-029

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