This cylinder head cover set includes all 5 cover pieces and applies to (and is not limited to) 50cc to 110cc engines. Most commonly used for 50cc to 110cc manual shift dirt bike engines. These parts are located on and around the cylinder head and when removed yields access to the rocker arms and allows for adjustments on the intake and exhaust valves etc. The small caps (2pcs) have a thread diameter of 29mm. The diameter of the large circular piece is 82mm.