Window balance replacement

A home owner from USA says:
I would like to order the following items but wanted to check if they are the right parts to order for my windows. Attached are photos of the old parts for your reference.

User submitted photos of a window balance.
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.

Now, as you can see, the only difference between these two Series 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 15-001 & 15-002
Comparison of 15-001 & 15-002
A quick learner says:
Hi Tom,

Thank you for your prompt reply.

I noticed that sash weight for both series is up to 30 lbs. But my windows are about 50 lbs. So how would any of these be able to carry the weight of the windows? Do you have a balance that could carry 50 lbs of weight?

Thank you,
Mary

Profile picture of Tom
Tom from SWISCO responded:
Wow, 50 pounds is a lot! Can you double check? Make sure to remove the sash completely from the window before you weigh it. Could you also give me the length of the metal channel and the stamp printed on it? Finally, what Series did you decide on?
A quick learner says:
Hi Tom,
Hope you had a good Thanksgiving and sorry for the delay. I was out of town for a while.
We need Series 390 / 15-001 and each of my window weighs 47 lbs therefore, we would like to order balances for 50 lbs windows. Yes, I know...it's unusual for an apartment.
The length of the metal channel is 38 inches and the stamp printed reads "37DS B.S.I. OP 47L". See attached but you would need to magnify the attached photo to see the information clearly.
I would like to order the following items:
- 8 units of balance
- 8 clips
- 4 parts of Top Sash Guide Pair (LH/RH). Product code is 18-159P

Thank you,
Mary
User submitted a photo of a window balance.
Profile picture of Casey
Casey from SWISCO responded:
Thank you for your patience, Mary. We are currently working on this, but I wanted to clear a couple things up. Are all eight of the needed balances for the lower sash? Also, we suggest sticking with 47 pounds, not 50. These are precise systems and it is possible for a balance to be too strong!
A home owner from NJ says:
Hello Donna,

Thank you for your response. Sorry, I have been traveling a lot so I was able to respond just now.

Yes, I need the lower sash for all eight of the balances for the right and left hand sides. Also, I will go with your suggestion with 47 pounds for the balances.

Thank you and let me know what the next step should be in order to process the order.
Mary
Profile picture of Casey
Casey from SWISCO responded:
Hi Mary,
Thanks for getting back to us! I'll email you a custom balance ordering link shortly.
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