Editing Axle (section)

==Terminology==
On cars and trucks, several senses of the word ''axle'' occur in casual usage, referring to the shaft itself, its housing, or simply any transverse pair of wheels. Strictly speaking, a shaft that rotates with the wheel, being either [[Bolt (fastener)|bolted]] or [[rotating spline|splined]] in fixed relation to it, is called an ''axle'' or ''axle shaft''. However, in looser usage, an entire assembly including the surrounding axle housing (typically a [[sand casting|casting]]) is also called an ''axle''.

An even broader (somewhat figurative) sense of the word refers to every pair of parallel wheels on opposite sides of a vehicle, regardless of their mechanical connection to each other and to the vehicle frame or body.  Thus, transverse pairs of wheels in an [[independent suspension]] may be called an ''axle'' in some contexts.  This very loose definition of "axle" is often used in assessing [[toll road]]s or [[excise tax|vehicle tax]]es, and is taken as a [[Proxy (statistics)|rough proxy]] for the overall weight-bearing capacity of a vehicle, and its potential for causing wear or damage to roadway surfaces.