New window balance

A quick learner from Berkeley, CA says:
I'm looking to purchase two new window balances, as one of mine broke. The Milgard window is 40.5" wide and 26.5" high, measuring the actual window that comes in and out. There balance is 24" when you measure the metal part, and it is 25" when you measure including the plastic ends.
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Casey from SWISCO responded:

Hello,

With this combination of attachments, you could have either the S380-24 or S385-24 channel balance. You’ll need to measure as shown below. The Series 380 has a 1" bottom attachment, and the Series 385 has a 1-3/32" attachment. 

You'll also need to locate the stamp code on the metal channel to choose the corresponding spring strength options for your replacement balances. Thank you and let us know if you have any other questions or concerns.

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

A quick learner from Berkeley, CA says:
Thank you, this is helpful. I must have the s380 since the ends is 1". I'm not able to find any numbers stamped into the metal, but I was able to find a printer marking- please see attached. Does this give any clue to the spring? If not, I'd there somewhere specifically I should look at for the stamp?
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Casey from SWISCO responded:

The 23-9 is the strength code but, unfortunately, it is from an outdated system that is no longer used. I would recommend weighing your window sash and following the chart shown under the S380-24 product description to choose the corresponding strength option.

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