The Dynatrac Differential Covers are about function and form. They are cast from our proprietary nodular iron for strength and durability. Strategically located RockRibs on the covers add more protection to vital internal components. These rockproof covers also add structural rigidity to the axle housing. The have thick, machined gasket surfaces for sure-sealing and an easy-to-access oil fill plug. Allen-head fasteners, which are less susceptible to damage from rocks are included. And, Dynatrac Pro Series Differential covers are made in the USA!