Pro - Alloy Mechanical Roller 1.660 Triple Valve Springs Howards Cams Pro-Alloy material is specially developed low stress, high endurance material. Howards Cams research and development staff spent many years of development, experience and testing to create a spring you can count on. Low fatigue rate compared to most roller springs on the market. Cycle tested to 12 million cycles with no breakage. Each spring is coiled using the most advance CNC winders in the industry. Each spring is then parallel ground, stress relieved and deburred. They are then shot-peened and heat-treated to our own very specific standards. These high standards are what it takes for a longer spring life, even in rough racing environment.