Torque transmission coupling

A torque transmission coupling, comprising:

• a rotation shaft portion;
• and
• a rotated shaft portion to which torque is transmitted from the rotation shaft portion,
• wherein the rotation shaft portion and the rotated shaft portion are coaxial and configured such that one of the shaft portions is loosely fitted to the other shaft portion,
• wherein between the rotation shaft portion and the rotated shaft portion in a radial direction, a plurality of cylindrical keys for transmitting torque are interposed in such a manner that they are arranged along an axial direction and at equal intervals in a circumferential direction,
• wherein the plurality of cylindrical keys are disposed in a plurality of key grooves formed in the rotation shaft portion and the rotated shaft portion, and
• wherein each of the plurality of key grooves has a spatial clearance with a corresponding one of the cylindrical keys, the spatial clearance allowing clearance of the rotated shaft portion relative to the rotation shaft portion in a θ direction.