The purpose of this work is to advance an alternative analytical solution of the pure drag flow in single screw extruders which is also applicable to intermediate values of the screw channel cross-section aspect ratio. The model is based on that of Li and Hsieh [Li, Y., Hsieh, F., 1996. Modeling of flow in a single screw extruder. journal of Food Engineering 17, 353-375] for the isothermal flow of a Newtonian fluid in a small curvature screw channel where the motion of the screw flights are taken into account in the boundary conditions. The resulting boundary value problem was solved analytically via the generalized integral transform technique (GITT). The model was validated against other models available in the open literature. The effect of parameters related with the screw geometry, i.e., the aspect ratio, the curvature ratio and the helix ratio, on the down channel flow rate is also explored in the manuscript. (c) 2008 Elsevier Ltd. All rights reserved.