The Action Army M14 Aluminum Alloy Cylinder Head features two o-rings to ensure your air compression stays tight to set the FPS you are looking for. A plastic cylinder head can crack over time from the constant impact it is receiving. This cylinder head has an aluminum construction that will hold up through thousands of shots and hits from the piston head. Replace your cylinder head along with other supporting parts in the gearbox to boost or retain the FPS of your airsoft gun.