Abstract: A drum for assembling tire components comprising a sliding body externally mounted on and engaged with a shaft so that it may move in an axial direction, and a cylindrical aggregate of circumferentially spaced apart segments externally mounted on the sliding body by an expander means so that the outer diameter of said cylindrical aggregate of segments is expandable and reducible by means of the backward and forward movement in the axial direction of the sliding body by a cylinder mechanism provided outside the sliding body. The expander means comprises tapered surfaces on the outside of the sliding body and the inside of each segment and an axially displaced annular piston and cylinder tube is operatively connected to the sliding body by means of connecting members.