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A half shaft is a drive axle that extends from a transaxle or differential to one of the drive wheels. There are two half shafts per drive axle, one for each wheel, each doing "half" the job.

Semiconductors have valence shells that are exacly half full and can conduct electricity under some conditions but not others. This property makes them useful for the control of electrical current.

Combustion is the burning of an air-fuel mixture to provide energy. It requires the presence of air, fuel, and a heat source to ignite the air-fuel mixture. In the internal combustion engine that powers automobiles and trucks the combustion happens inside the engine utilzing a fuel like gasoline, diesel fuel, or natural gas.

Wrenches are used to provide grip and mechanical advantage by applying torque to turn objects (or to keep them from turning). The longer the wrench, the more torque that can be applied. Wrench ends are available in two primary types, open-end and box-end. A box-end wrench encloses the bolt head and is useful when more torque is needed or to maintain contact in difficult to reach locations. An open-end wrench is designed for speedily loosening easier to reach fasteners. Wrenches that feature one open and one box end are called combination wrenches and adjustable wrenches feature an open end with an adjustable width.

A molecule is the smallest multi-atom particle of an element or compound that can exist and still retain the characteristics of the element or compound. The molecules of elements consist of two or more similar atoms, the molecules of compounds consist of two or more different atoms.

A person's genotype is their genetic makeup and includes both dominant and recessive alleles. Phenotype is how the genes express themselves in physical characteristics.

Torque measures force applied during rotation: τ = rF.  Torque (τ, the Greek letter tau) = the radius of the lever arm (r) multiplied by the force (F) applied. Radius is measured from the center of rotation or fulcrum to the point at which the perpendicular force is being applied. The resulting unit for torque is newton-meter (N-m) or foot-pound (ft-lb).

A clamp applies pressure to prevent two objects from moving relative to each other, for example, to keep to pieces of wood together while the glue between the dries. A clamp is commonly made of metal and shaped like the letter C with a perpendicular flat-edged plate providing variable pressure between it and the top of the C as a screw to which it is attached is tightened and released.

The camshaft is linked to the crankshaft through a timing belt and regulates the opening and closing of the intake and exhaust valves in each cylinder in time with the motion of the piston. An engine designated OverHead Camshaft (OHC) locates the camshaft in the cylinder head. An engine with Double OverHead Camshaft (DOHC) has two camshafts, one to regulate the intake valves and one to regulate the exhaust valves.