A single screw extruder (E) for the extrusion of food or feed, comprising in the direction of flow of a product to be extruded: i) a processing section (8); ii) a bypass outlet (B); iii) a valve plate (V); iv) a die plate (D); and iv) a cutter (6). The flow of product can be directed through the valve plate, under normal operating conditions of the extruder (E), and through the bypass outlet (B), during start-up of the extruder (E) or for maintenance purposes, downstream of the valve plate (V). The valve plate (V) is arranged on or in a mounting plate (M). The cutter (6) and the mounting plate (M) are provided with interacting guiding mechanism that prevent rotation of the cutter (6), vis-à-vis the mounting plate (M); and the cutter (6) and the mounting plate (M) are mechanically fastened to each other with rotational locking mechanism.