Gears, bearings, springs, fasteners etc. are some typical machine elements used to build machines and mechanical systems. These elements are used for performing one or more of functions such as, to transmit motion, to support moving members, to store energy, to join two components etc. The continuous miniaturization and the need for mechanical systems having sizes of a few nanometers have led to new but challenging issues in design and manufacturing of these machine elements. Carbon nanotubes have a potential to be used as machine elements in multiple roles for building mechanical systems at a nano level. This paper explores the use of single-walled and multi-walled carbon nanotubes in building a nano-mechanical system such as gearbox . The paper presents a conceptual design of a gearbox completely made of carbon nano tubes and discusses its feasibility and realizability. The paper also discusses future directions of research in building nanomachines and nano-mechanical systems using carbon nanotube based machine elements.