There are a few different kinds of pencil sharpeners; mechanical prism sharpeners, blade sharpeners, cylindrical cutters and electric sharpeners are the most common. The first patent on pencil sharpeners was granted in 1828 to Bernard Lassimone, a Frenchman. Since then pencil sharpeners have undergone various design changes, but the core function and components have more or less remained the same.
The housing is the outer shell of the pencil sharpener. It supports, holds and contains all the inner components. In prism sharpeners, the housing also holds the blade in place. In a cylindrical cutter, the housing is simply a cover for the mechanical parts inside.
The opening or mouth of the pencil sharpener is where the pencil is inserted. The mouth is typically slightly larger than the pencil and is conical in shape, getting progressively deeper. The walls of the mouth are typically made of the same material as the housing; in most pencil sharpeners the housing and mouth are one piece. Part of the wall of the mouth is made up of the blade, the piece that does the sharpening.
In prism sharpeners, the blade is a small piece of flat steel with one edge sharpened. The blade is positioned on an angle so that when the pencil turns in the sharpener the edges of the pencil scrape against the blade, shaving off the edges of the pencil and making it sharp. After time, the blade can become dull and may need to be sharpened or replaced.
Wall-mounted mechanical sharpeners use cylindrical gears instead of a blade. The pencil is inserted into the mouth of the sharpener and two gears grind against the pencil to sharpen it. The gears are activated by a hand crank. These types of sharpeners are typically found in schools.