The invention relates to a printing unit (01) comprising at least two side frame parts (11; 12), whose the distance relative to each other can be modified in a horizontal direction and which each receive at least one printing group (04) or parts of a printing group (04) and of which at least one side frame part (12) can be moved between a closed functional position, in which the side frame parts (11; 12) are moved together and fixed relative to one another, and a open position, in which they are spaced from each other. In order to fix side frame parts (11; 12) relative to one another, at least one closure device (31) is provided, comprising a cylinder (32) pretensioning the side frame parts (11; 12) into the closed functional position, wherein the cylinder (32) comprises a piston rod (34)carrying out a stroke movement, wherein the closure device (31) is designed as a swivel tensioning element (31), wherein the piston rod (34) is arranged such that it carries out a pivoting movement about a longitudinal axis of the piston rod (34), in addition to the stroke movement, and/or the piston rod (34) can be pivoted about a longitudinal axis of the piston rod (34), in addition to the stroke movement.