THESE VALVE COVERS ARE TIG WELDER SHEET METAL ALUMINUM . THEY FIT ALL ROLLER ROCKERS , STUD GIRDLES , AND ARE POLISHED FOR EASY CLEANING . THEY ALSO ARE TIG WELDED TO A FLANGE FOR ADEGUATE GASKET SEALING . EXCELLANT FOR THAT OUTSTANDING RACE LOOK !!!. THEY ARE DRILLED FOR PUSH IN BREATHERS . THEY ALSO COME WITH RUBBER GROMMETS/BAFFLE IN ONE , ONE BREATHER IS A PVC VALVE . BREATHERS INCLUDED WITH BOLTS