A rectangular baler comprising a bale chamber； a plunger； a guide system adapted for guiding the plunger, comprising 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 said mounting piece has a mounting surface which is fixed against a guide surface of a member； said mounting piece and said member having an elongated slot and a through-hole, respectively, or a through-hole and an elongated slot, respectively； said threaded shaft extending through said through-hole and said elongated slot and having an axis making an angle with respect to said guide surface which is smaller than 90 degrees.
