Abstract: A unistage drum (1) for producing an agricultural tire (2), the drum (1) having a fixed central body (16) for supporting a relatively thin central portion (11) of the carcass (3) of the tire (2), and two movable half-drums (15) located on opposite sides of the central body (16) to support respective thicker lateral portions (12) of the carcass (3). Each half-drum (15) has a respective expandable bead clamping device (23), and is, at least along a portion projecting outwards of the relative bead clamping device (23), of a diameter (D2) smaller than the diameter (D1) of the central body (16) so as to compensate for the differences in thickness between the central portion (11) and the lateral portions (12) of the carcass (3).