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Patent Pending TSENTSIPER’S KEY JOINT 1) 20% economy of metal consumption for making reduction drive, transmission, gearbox, dropbox, chaindrive, beltdrive, and other mechanisms which transmit the torque. 2) You don’t need the hub anymore. 3) There are no shear or bend deformation. 4) Key joint details don’t make any stress concentrator. 5) Construction of key joint is diametric. The invention relates to the field of mechanical engineering, namely, to key joints that are widely used in engineering. The key joints are the detachable joints of the external member (gear wheel, sheave, sleeve pipe, balance wheel, hub, cam, etc.) and internal member (axis, shaft) for the torque transmission using a typical part of the key machine. Most key joints constructions are standardized or normalized. Most common are standard (ISO, GOST) unstressed key joints with prismatic keys which have a rectangle in cross section. These key joints in machine elements and mechanisms make up more than 90%. Numerous constructions of key joints are known, most of which are standardized (GOST 8788, 8789, 8790, 8791, 8792, etc.). Calculation and choice of the steel grade of the keys are made, as a rule, by checking the stresses on the crushing and comparing them with the tolerable stresses for a given steel grade. It is related to the fact that calculation of the main stresses on the shearing strain (shift) and bend, to which the keys are subjected and in which the allowable stresses are lower than the allowable stresses for crushing, have been carried out during standards development. Almost in all types of key joints, it is required to perform sufficiently deep and wide grooves in the shafts for the mortise (common name) keys, which greatly weakens the cross-section of the shaft, especially of hollow shafts. The weakening of the shaft is based not only on a reduction in its cross section, but also on a significant concentration of bending and torsional stresses caused by the keyseat. It is well known that in order to consider this at a given torque it is necessary to increase the estimated shaft diameter by about 8-10%. All of the above refers to the main disadvantages of such key joints. In addition, to ensure the equitability of stresses as to the cross section of the key, and along its length, when making the key seat on the shaft, it is necessary to ensure strict parallelism of their axes.