Gearing devices generally used in transmittin motionbetween two axes which are operating neither inparallel nor  intersecting each other are worm gears,hypoid gears and screw gears of which worm gearsoperate in line contact while the others in pointcontact. Because of its line contact, a worm gear has supe-riority in road capacity, even though the  contact areaof a hypoid gear has been widened by the latesttooth cutting method.

On the  other hand a worm gear has a defact to havea high relative sliding rate at its contact point. Nevertheless, a higher load capacity and efficiencyare expectable in an Hourglass Worm Gear, becauseof its unique interlocking condition which enables, ashas been proved in hydrodynamics, output of a higherpressure in a given oil film, through a specially design-ed relative curvature of tooth face at contact pointand sliding direction.