In a torque transmission system, plural engagement pieces elastically deformable
are formed integrally with an outer peripheral portion of a circular portion of
a center hub to be engaged with an inner periphery portion of a pulley. A bridge
portion of the center hub is disposed to be broken when a torque large than a predetermined
torque is applied there to. Since the engagement protrusion pieces are engaged
with a part of the pulley, it can prevent the center hub from being removed and
falling when the bridge portion of the center hub is broken.
