28mm diameter. Filler cap seal. W/O HIGH OUTPUT. A Sealing device that prevents leaks at the Engine Oil Fill Tube. Engine Oil Dipstick Tube O-Ring. Engine Oil Filler Cap Gasket. Engine Oil Filler Cap O-Ring. Engine Oil Filler Cap Seal. Engine Oil Filler Tube Seal. Exc.Performance Package. Inner Diameter 28mm. Performance Package. Engine Fill. inlet. Engine cover grommet. Engine Dipstick O - Ring. Engine Gasket. Engine Pipe O - Ring. Included with: Cap, Cap assy, Engine cover, Filler Cap, Filler Tube, Included with Filler Cap, Oil Filler Tube, Oil inlet Tube, Valve cover.