You won't break this cover, we guarantee it. If you do, we'll replace it (see warranty terms). Made of 3/8 inch cast steel, painted black inside and out, this heavy duty cover is designed to protect your differential and all its working parts for as long as you own your vehicle. This cover even has reinforced protection for the fill plug. All mounting hardware and instructions are included.. This Rugged Ridge Heavy Duty Differential Cover for Dana 35 axles. Constructed of 3/8 inch cast steel.