Moving parts are the components of a device that undergo continuous or frequent motion, most commonly rotation. "Parts" only include the mechanical components which does not include fuel, or any other gas or liquid. The moving parts of a machine are by far the most common cause of failures because they receive the most wear and tear.^{[citation needed]} Because of this most engineers attempt to reduce the number of moving parts. An example is the switch from Turboprop to ramjet. A schematic diagram showing the operation of a turboprop engine. ... A ramjet, sometimes referred to as a stovepipe jet, is a type of jet engine. ...