Spring used since mid 1980's on Autotrol 155, 255, 163, 168, and others.
Most Flapper Valve problems are best fixed by replacing the Flapper Valve Discs and NOT the springs. Springs should only be replaced when physically broken.
If your Valve is over 20 years old, it would be wise to replace the Upper Valve Module ( part # AP24NC
if you have the Series 155 or 255 Model ) if the Flapper Valves are not closing properly.
Cross Reference Part Numbers = 23F-2 and 100b214-001