Amesbury Truth Universal Constant Force balance for Egress Applications
Used primarily with Single Hung or Double hung sliding vinyl windows 

Interlocking Coils can be mixed together to match appropriate sash weight 
Available in several poundage: 3, 4, 5, 6, 7, 8 pounds
Coil Width: .394 ( 10mm) 25/64 inch ( Slightly over 3/8 inch ) 
Pocket Width: 1-1/4 inch (31.75mm) 1.25 
Weight Markings: 3.0 - 8.0 pounds( weight) , 35" ( Max Travel) 
Sold as parts to Repair or make balance - Coils, support covers, brake shoes and pivots sold separately

NOTE: The 3/8 egress used a curved top plastic support cover. 

Related Parts: 
533025 - 3/8 Egress Coil 3-6 pounds
533026 - Brake Shoe 1-1/4 Pocket, Side Locking, Tall 
533027 - Brake Shoe 1-1/4 Pocket, Back Locking, Tall
533028 - Brake Shoe 1-1/4 Pocket, Side Locking , Short, Heavy Duty 
533029 - Brake Shoe 1-1/4 Pocket, Side Locking, Short, Standard
533008 - Pivot Bar, T-Head
533019 - Pivot Bar Retainer
533036 - Support Cover, Dual
533037 - Support Cover, Triple
533038 - Support Cover, Quad