A packaging machine with a carousel with horizontal axes, particularly suitable for packaging rolls of paper or packs of paper serviettes or other solid products of variable size, of the type that comprises a plurality of identical seats on the same carousel, angularly equidistant from each other, radially open towards both the outside and the inside and each formed by a longitudinal wall fastened perpendicularly to said carousel and by a parallel and opposite wall, the distance of which from said fixed longitudinal wall can be adjusted to ensure that, with a movement parallel to the axis of the carousel, a product of variable size with its wrapping sheet can be inserted between these walls, and wherein the same seats comprise, between said longitudinal walls, two transverse walls designed to cooperate with the ends of said product with the wrapping sheet inserted in the same seats, which for this must have an adjustable reciprocal distance, whereby at least one of these transverse walls is connected to means for adjusting the distance from the other transverse wall, characterized in that said adjustment means comprise, for each said wall, respective internal threads and respective slides sliding on respective rectilinear guide means, directly or indirectly supported by the table of the carousel and parallel to the movement of the associated walls, with two sets of screws being provided parallel to these guide means that cooperate with said internal threads, which are also rotationally supported, directly or indirectly, by said table, these screws being kinematically connected to each other by associated means to ensure that by acting on one of the components of these connection means, the adjustment of the dimensions in length and in width of all the seats is performed in a centralized, rapid and precise manner to adapt them to the different sizes of the products to be packaged.