20+year old balance

A handy person from Antelope, Ca. says:
# on balance is 2730 and a backwards/upside down letter K. Also perpendicular to the 2730 # is the # B.S.I(letter I)as best as I can make out. Thanks in advance for your help.
User submitted photos of a window balance.
A handy person from Antelope, Ca. says:
My chanel measures 27 1/2". Do I order 27" or 28"?
Profile picture of Tom
Tom from SWISCO responded:
Hey, thanks for posting. I've narrowed this down to two possible channel balance Series: either our Series 351 or our Series 390 balances.

Now, as you can see, there is only one difference between these two Series, and that is their bottom shoe. The Series 351 uses the 15-002 while the Series 390 uses the 15-001. I can't quite tell what you have based on your pictures, though. Please carefully compare their dimensions to your own hardware and see which is a better match.
Comparison of <a href='Channel-Balance-Shoe/pd/Replacement-Sash-Support-Channel-Balance-Shoes/15-001'>15-001</a> & 15-002

As for the top sash guide, check out our 18-008 and see how well this matches.

I'm not sure about the length of the channel. Based on your stamp, it should be 28" long. Does it look like it has been cut down? Are both channels the same length?
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