Piston

A piston is a part that, together with a cylinder and a cylinder head, forms a combustion chamber and takes on reciprocating motion inside the cylinder on each intake, compression, combustion, and exhaust stroke. Its main role is to receive expansive power and transfer it to a crankshaft through connecting rods.
The upper part of a piston is referred to as a piston head, and the lower part is referred to as a skirt.
Furthermore, the skirt part includes a piston pin boss for attaching a piston pin.

Since the piston is constantly exposed to high temperatures and high pressure and must also withstand high-speed reciprocating motion, various innovations have been made in its shape and structure.
For example, because the piston head part is heated and expands significantly it has a smaller diameter than the skirt part, and the diameter of the skirt part is also smaller toward its upper part.