PURPOSE: To achieve the dynamic balance of a transmission gear to prevent vibration by offsetting elements belonging to a portion inward of the gear, so that the gear is unbalanced.

CONSTITUTION: A driving element 10 is secured to a tulip member 14 serving as a part of a triport type joint 20. The member 14 comprises three pairs of lace ways 22 that work in collaboration with three spherical rollers 24 placed on three trunnions 25 which are 120 degrees spaced apart from one another. A block 26 is supported at the spline end 27 of a terminal member 28, and the other end 29 of the terminal member 28 has a large diameter and is welded to a hollow shaft 30. The portion of the terminal member 28 between the spline end 27 and the welded region of the hollow shaft 30 is slightly offset with respect to the X-X axis and unbalanced. This intentional unbalance permits clearance to be absorbed during rotation because of relative positions that are always the same.