Compact planetary reducer for mechanical transmission, common field of application being mobile machinery for the lifting and transportation sectors but also more generally in construction, shipping, agricultural and nautical sectors. Other specific uses are in rotating concrete-mixer pumps, excavators, mobile cranes and cranes mounted on trucks and aerial platforms. Planetary reducers are widely used in industrial plants of the most differing sectors: sheet metalworking, iron and steel, plastic processing, water treatment, chemical, energy, mining, other processing plants