Identifying Window Balance with Stamp 39 9 GW CMC 11

A quick learner from Richmond, VA says:
Hi my name is Spencer and I need help identifying a window balance for replacement. The stamping on it is exactly as follows: "39 9 GW CMC 11"

Thanks for any help with this and feel free to e-mail me for anything else you need to know to identify which set of window balances I would need to purchase
User submitted picture of channel balance 39 9 GW CMC 11".
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Tom from SWISCO responded:
Thanks for posting in our discussion board, Spencer! We will need a bit more information before we can identify an applicable replacement for your balances.

Can you give us the length of the metal channel portion of your balance in inches? Please do not include the attachments in this measurement.

Can you also refer to the following chart and identify which of these bottom shoes matches your own? I can see that yours doesn't have any wings, but the length of the shoe is vital.
A SWISCO guide to identifying balance shoes.
A quick learner from Richmond, VA says:
Metal balance measures to 40" from metal end to end and the shoe length is 1 1/8".
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Tom from SWISCO responded:
Thank you for the information! It appears that your balance would be a Series 390. Unfortunately, I'm a little unsure of the stamp option at this point; 3990 is a bit peculiar for this Series. If at all possible, can you please remove your sash and weigh it? Knowing the weight of the sash will help us determine what stamp option would be best.
A quick learner from Richmond, VA says:
Weighs in just under 40lbs 37-38 lbs to be more precise
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Paul from SWISCO responded:
Thank you for posting! A Series 390 with a 40" channel and a 3960 stamp option will have to be custom made. Please take a look at this Custom Made Channel Balance Form that I have started for you and fill out the rest of the information.

A S390-40 with a 3960 stamp option will carry a window sash weight range of 35 through and including 39 pounds.

This information is based on 2 balances per sash. Balances are designed assuming friction in the jamb weather-strip will carry a portion of the sash weight. Suggested sash weights are approximate.
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