A tool for assembly on a drum (1) to form a rotatable unit to be placed in journalling equipment for rotation of the unit, said drum (1) comprising a cylindrical sleeve (7) and two end pieces (11, 12) and designed to carry a coil (5) of a flexible object (6), such as cable, said tool comprising two support and bearing elements (17, 18), each with a hub (21), a plurality of support arms (24) and a concentric support member (27) for centering the drum; and also a connecting member having a shaft (19) extending through the sleeve and said hubs (21), and anchoring means for anchoring the support and bearing elements to the shaft (19) while at the same time securing the sleeve (7) against axial displacement in relation to the shaft. According to the invention, the support arms (24) are arranged to abut the end pieces and have free ends (33) located radially inside the outer circular edge (37) of the end pieces so that the support arms (24) are not in contact with the ground when said unit is resting on the ground by means of the end pieces of the drum.