Replacement Gorrell window balance

A landlord from Bluefield, WV says:

I have a 150 unit apartment complex with Gorell windows and we are running out of springs. Since they are no longer in business i have had one heck of a time trying to find parts. I have found all the balance parts I need on here but i'm not sure what lb spring I need. On the coil I have now it has 5FD stamped on it, so I assume I need 5lb but i'm not sure. How would i get this info so that i buy the right one? Also do they come all together like in the picture I provided or do i have to put them together myself?

Gorrell window balance 5FD
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Tom from SWISCO responded:
Thanks for posting. It might be a safe bet that you need an S180-5, but a good way to check is to weigh your sash. Each S180-5 can carry 5 pounds each, so four altogether (two on each side) can carry a 20 pound sash.

These balances do not come fully assembled. If you need the other parts shown in your picture, see our 15-087, 15-086, and 16-024.
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