A blade or contrast blade (1) which can be used particularly for example in machines for shredding cereals and/or fibrous material, composed of a plate (16) which has a first sharp perimetric edge (17) and, on the opposite side, a second perimetric edge (25), which are mutually connected by a third front edge (18). The third front edge (18) is slidingly and rotatably associable at an adapted first rivet (23) which protrudes from a support (24). The second perimetric edge (25) instead can be locked temporarily, upon a rotation imparted to the plate (16), at an adapted second rivet (30) which protrudes from the support (24).
