Chrome plated aluminum. Complete rockerbox set for one cylinder head. With breather passages and umbrella valves for late model head breathing Evo; for earlier case vented models; just don”t use the umbrella valves. Includes mounting hardware; umbrella valves and gaskets. Includes gaskets. Note: Rocker cover sets are for for late head vented models. Will fit early 84-91 B.T. crankcase vented models when the umbrella valve is not used.