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Piston refers to a component of reciprocating engines, reciprocating pumps, gas compressors, and pneumatic cylinders, among other similar mechanisms. It is the moving component that contains a cylinder and is made gas-tight by piston rings.

Pistons are light enough to reduce inertia loads on the bearings. Any object in motion resists any effort to change its speed or direction of motion. When a piston stops at the top dead center (TDC) or bottom dead center (BDC) and starts to move in another direction, it loads the bearings. 

Pistons are made of aluminum because it is light metal Most automotive engines use full slipper pistons. The skirts are cut away to save weight and to make room for the counterweights on the crankshaft. Many pistons are plated. They are given a thin coating of tin or other material Which helps prevent scuffing during break-in.

Aluminum pistons are either forged or cast, Cast pistons are made by pouring molten aluminum into molds. Forged pistons are hammered out from slugs of aluminum allot,