in an apparatus for producing particles of thermoplastic material by extruding material in a plastic state through orifices in a die plate and thereafter cutting the extruded plastic material into crumb upon exit from the orifices , an air supply is coupled to a cutting chamber for providing a stream of air across the face of the die plate to cut and convey the crumb away from the orifices . the cutting chamber is arranged to include a restricted throat having an exit area in close proximity to the orifices and a further portion for providing an accumulation zone adjacent the orifices , the accumulation zone having a cross - sectional area which increases from the exit area of the throat to a product discharge zone remote from the orifices in a downstream direction .