Pre-Assembled 984 Series constant force balance assembly with interlocking tandem coil springs. 
The 984 Series Universal Dual , Triple, and Quad Coil Balance with metal spring clip side locking brake fits single hung or double hung vinyl windows with standard 1-1/4 inch wide pocket.  

Application: Balance system for vinyl window  
Pocket Width: 1-1/4 inch 
Coil Thickness: 1/2 inch 
Brake: Side Locking Spring

Coil Length: 35 inch  
Number of Coils: 2 
Weights: 11 - 18 pounds 
Number of Coils: 3
Weights: 19-24 pounds 
Note:  
Any combination of coil springs that equal the desired weight will work.  
Example: The Tandem 12 pound weight could be 6/6 or 7/5