Pre-Assembled 985 Series Centurion constant force balance assembly with 3/4 inch wide coil spring.
The 985 Series Universal Single Coil Balance with metal spring clip side locking brake fits single hung or double hung vinyl windows with standard 1-1/4 inch wide and 3/4 inch deep pocket. 
The Centurion 3/4" Constant Force balance uses Interlocking Coil Spring Balance in Singles, Doubles, Triples and Quads.

This item is discontinued and limited to existing inventory. Replace with #533052.

The interlocking coils allow for multiple combinations of singles to meet a variety of sash weights

Application: Balance system for vinyl window 
Pocket Width: 1-1/4 inch (32mm)
Pocket Depth / Thickness: 3/4 inch (18.95mm) .746
Length: 
Brake: Side Locking Spring Clip
Number of Coils: 2
Window travel: 40 inch (1016mm) 
Weight Code: See image / # stamped on Spring 

Related Parts:
Amesbury 985 Centurion 3/4" Balance 
533072 - Dual Interlocking Coils
533075 - Brake Shoe
533076 - Individual Coils
533078 - Double Coil Cover