1. Mitsui Petrochemical Industries (1973) Method of and apparatus for treating the outer surface and inner surface of a pipe of a thermoplastic resinous material produced by extrusion. US Patent 4,159,889
2. Dynamit Nobel AG (1975) Process and apparatus for the extrusion and calibration of an elongate synthetic thermoplastic plastics member having a chamber extending lengthwise thereof. GB Patent 1,529,370
3. Gneuss, D (1982) Process for sizing pipes or tubes made of flexible plastics material and sizing device for carrying out the process. DE Patent 3,243,140
4. Gas Injection Ltd. (1999) Extrusion sizing/calibration dies with gas pressure control. GB Patent 2,354,965
5. Labaig JJ, Fenie M, Glotin M (1986) Extrusion Rilsan à grande vitesse. Technique ATO. Project report, Centre d’Etude de Recherche et Développement, Arkema, Serquigny, France