A rectangular baler including a bale chamber； a plunger； a guide system including a guide assembly for aligning and supporting the plunger in a transverse direction； each guide assembly including a mounting piece with a guide element, a threaded shaft； wherein the mounting piece has a mounting surface which is fixed against a guide surface of a member； the mounting piece and the member having an elongated slot and a through-hole, respectively, or a through-hole and an elongated slot, respectively； the threaded shaft extending through the through-hole and the elongated slot and having an axis making an angle with respect to the guide surface which is smaller than 90 degrees.
