Single-screw extruders use one-piece extrusion screws made either of chrome steel, with nitriding heat treatment, or with anti-wear and/or anti-corrosion alloy coating depending on the plastic material treated. The extrusion cylinders have a different L/D ratio depending on the production process for which they are intended, and can be thermostated either with air, through the use of electric fans, or with water/oil through the use of a special control unit. The basic materials for the construction of the cylinders are special chrome steels, subjected to nitriding heat treatments, or bimetallic steels with anti-wear and/or anti-corrosion alloy coatings.