Abstract: A single screw extruder, comprising a rotatable core means in an extruder barrel, is provided with spaced-apart discontinuous helical flights arranged on the rotatable core means with each flight centered in the channel formed by the preceding flights, the flights being formed by lands on the core means, and each land having a traversed axial length of about one diameter unit of the core means. The extruder is particularly useful in filler compounding of solid polyolefins, the blending of different polyolefins, and the reacting of monomers with polyolefins such as in extruder grafting.