balance with nonstandard? numbers

A quick learner from San Francisco says:
I need a couple of replacement channel balances and want to find the appropriate matching part and get a price. The stamped numbers/letters, which don't seem to correspond to your system, are: 26 9 KV CMC 2. The window (lower sash, metal frame, double glazed) is approx. 46" wide x 29" high x 1-5/16" thick, and weighs 25 lbs. The balance width is 1/2". It looks like your Series 380 or 385. (I can't tell them apart ... what's the difference?) I'm a renter, but don't particularly want to involve my landlord. I've replaced similar balances before. The nonworking balances failed due to broken cords to the pulleys, and I wonder if that was age and normal wear or due to a mismatched weight specification. Probably they could be repaired but it looks difficult and I don't feel up to it.
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Tom from SWISCO responded:
Thank you for posting. The major difference between the Series 380 and Series 385 lies in their shoes. The Series 380 uses our 15-005 while our Series 385 uses our 15-004. Which one more closely resembles your own?
Comparison of 15-004 & 15-005
Once you've determined whether you have the S380-27 or S385-27, you can compare the weight of your sash to the options for each to see which would be better.

Check out the video below to see the best method of how to replace these balances. It is a very simple procedure and you should be done before you know it.
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