The cylinder head is one half of the compression cycle of the cylinder set. It is used as conduit for air and controls the flow of air out of the cylinder. It allows a volume of air from the cylinder to be compressed through the nozzle, there by propelling the BBs out of the hop up chamber.
A cylinder head in an airsoft gun enhances airtightness as air is compressed in a cylinder, with a piston's travel and cylinder together achieving maximum air compression. Modify's MOD24 cylinder head has special design to enhance compression of air in the overall operation of airsoft guns.