This standard includes information on design, lubrication, bearings, testing and rating for single and double helical external tooth, parallel shaft speed reducers and increasers. Units covered include those operating with at least one stage having a pitch line velocity equal to or greater than 35 meters per second or rotational speeds greater than 4500 rpm and other stages having pitch line velocities equal to or greater than 8 meters per second. Annex material includes discussions on service factors, rotor dynamics, efficiency and newly configured purchaser's data sheets.