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.