Abstract: A device (5-120) for joining the plies (1-2) of tires in the green state, in which the plies (1-2) are joined together along adjacent edges (4) by the joint action of a first (87, 93) and a second (36, 42-126) plurality of pairs of rollers disposed one facing the other, the first being above and the second being below the said plies (1, 2) and having a V-disposition with vertex along a junction line of the said edges (4); the rollers of the first plurality of rollers (87, 93), which are externally serrated, being supported by a support body (7) which is adjustable both in height and about a horizontal axis with respect to the second plurality of rollers (36, 42-126), and being connected to an operating unit (101) carried by the said support body (7), with the rollers of each pair being rigidly connected angularly together and being disposed with their ends in contact along a generatrix.