Abstract: Apparatus for cutting thermoplastic filaments or rods with multiple blades in a granulation head of the type which is completely immersed in a cooling liquid, the blades acting with an extrusion die having extrusion orifices arranged in one or more rings centered on the axis of the die and coaxial with a rotary cutting means carrying cutting blades, wherein the cutting blades have an extrados surface inscribed within a regular convex polygon having an apex angle of 7.degree. or less and an intrados surface having a point of inflection situated at a distance between one quarter and one half of the width of the blade, the remainder of the intrados beyond the inflection point having a profile pattern similar to that of the extrados, and methods for chopping thermoplastics with such apparatus.