A power transmission socket for bobbins comprising a pair of coupled members, a first of which is connectable to a bobbin and second of which is connectable to a driving base of a spindle. The members are coupled to each other such that they can turn relative to each other a predetermined small distance for gripping the spindle. The members are provided with integral projections, respectively, and form complementary recesses rotatably displaceable relative to corresponding projections which have a spindle gripping surface and an outward engaging surface urging projections displaced inwardly as well as in the direction opposite to that of the rotation of the spindle causing the gripping surface to grip the spindle.