series Series 390 Channel Balances

A quick learner from Monroe, WA says:
I have a 5 1984 Milgard single hung aluminum windows with short sashes - the counter balance appears to be the 390 series, but the tube length is only 9".

sash weight is 4-5 lbs.

I probably also need the top sash guides #18-008

Your help is appreciated
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Tom from SWISCO responded:
Thanks for posting! Just to confirm, when you're measuring the balance length, you're measuring the entire metal channel, correct? 9" is very small, and I'd like to confirm. Also, are there any stamps or marking printed on the channel?
A quick learner says:
Yes they do measure just 9" on the metal portion. These windows provide expansive views so i think the builder kept the sash short to obstruct them as little as possible.
The channels are stamped with "08 D" along the axis and "B.S.I" across the axis after the D. There are no other markings.

two photos attached, the secobd one should have enough detail to see the markings.

Thanks for any help
User submitted photos of a window balance.
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Tom from SWISCO responded:
Thank you! This balance will have to be custom made. To begin, please take a look at this Custom Channel Balance Order Form that I have started for you and fill out the Contact and Shipping sections. One of our representatives will be in contact with you shortly thereafter.
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