Usually has a built-in gasoline engine as prime mover, flushing being provided by the exhaust gases or by compressed air produced in the machine. Total weight varies between 50 lb and 120 lb (22.7 kg and 54.4 kg). Motor hammer drills are used for oddjob operations, on forest roads, in prospecting, etc., where it is not worthwhile to lay air supply lines on account of transport difficulties or insufficient volume of work.