Fleece Performance, Duramax Rocker Bridges. Fleece Performance billet rocker arm bridges for the GM Duramax. These bridges offer a massive 2.5-time strength improvement over factory bridges. Machined from billet 8620 steel, the bridges are surface ground for flatness, feature improved oiling to the valve stems, and are case hardened and carburized for strength. Includes 16 bridges.