Coil balance System

A home owner from Illinois says:
Hi I am looking to replace the window balance systems in 10 windows in my house. My house was built in 1996. I currently have double coil window balances, one coil is #5, I can't see a stamp on the other coil. The windows are single hung vinyl windows, can't tell the manufacturer. The pivot block is 1-1/4" x 1-1/2" x 1/2". The window sash weighs 18 lbs. Do you have a replacement coil part that would work? Can I replace the window balance with a single coil system, or do I need to use a double-coil system?
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Tom from SWISCO responded:

Your balance system has been discontinued by the manufacturer and has been replaced with the 15-140 balance shoe and Series 150 coil spring. 

We also sell the 15-144 bushing cap, 15-143 bushing, and 15-145 barrel.

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