Frictional forces (for temperatures less than the melting or devitrification temperature) and viscous forces (for higher temperatures) have important roles on solids conveying and melting processes in plasticating single-screw extruders. These forces are related to the shear stresses at polymer-metal interfaces. For temperatures at which the frictional forces are the main factor for the shear stresses, it is experimentally difficult to obtain the shear stresses at the polymer-metal interface. The interpretation of the data has further complications due to the frictional energy dissipation at the polymer-metal interface. An instrument called the Screw Simulator was used for further understanding of shear stresses at the polymer-metal interface and comparison of melting fluxes of different resins. This article presents the shear stress and melting flux measurements for low density polyethylene (LDPE), linear LDPE (LLDPE), acrylonitrile butadiene styrene (ABS), and high-impact polystyrene (HIPS) resins as a function of sliding velocity and interface temperature at a fixed pressure of 0.7 MPa. The relationship between the experimental data and the extrusion process is also discussed. POLYM. ENG. SCI., 49:471-477, 2009. (c) 2009 Society of Plastics Engineers