This standard specifies the basic parameters, lubrication and load-carrying capacity of PWU, PWO, and PWS three series of planar double-enveloping toroidal worm reducers (hereinafter referred to as reducers). This standard is applicable to the reduction transmission of mechanical equipment in metallurgy, mining, lifting, transportation, petroleum, chemical industry, construction and other industries. The working conditions applicable to this standard: a. The intersection angle of the two shafts is 90°; b. The rotational speed of the worm does not exceed 1500r/min; c. ℃, the lubricating oil should be heated or cooled accordingly before starting); d. The worm shaft can run forward and reverse.