The purpose of this section is to describe world standards for the most commonly used power source in industry — the electric motor — and some of the important power transmission components, such as transmission chains and sprockets, endless belt drives, metric module gearing, splines and serrations, and keys and keyways. Some standards for these items have been based on the metric measuring system, and the others on the customary inch system. The main differences will be pointed out in this chapter to facilitate worldwide interchangeability of parts. A number of ISO and IEC standards have been issued on the...