Abstract: A screw plastifying and conveying device includes a screw (5) which has a pull-in zone (I) of constant pitch volume (V.sub.0), a first compression zone (II), and adjacent thereto, i.e. in the injection side, a second compression zone (III). The compression ratio (V.sub.1 :V.sub.0) of the second compression zone (III) is between 1:1.0 and 1.2, while that of the first compression zone is between 1:1.6 and 1:4. This makes it possible, by underdosing, to reduce the melt volume in the second compression zone, thereby achieving stable conveying action over a wide operating range. Molded parts with minimal internal tensions and e.g. also molded parts of glass-clear material with unobjectionable optical properties can thus be produced.