Comminution in mineral processing must be tailored to the final product requirements. In many cases the requirement for comminution is to generate the maximum amount of size reduction in the minimum number of equipment stages. There are however certain applications where maximum size reduction, or fines generation, are not desirable. In such cases, and where the material characteristics allow, the application of twin rolls, toothed mineral sizers is often advantageous. This paper examines the function of an MMD 625 mineral sizer in terms of its mechanical design parameters and its interaction with the feed material. Using the understanding developed during the study a mechanistic predictive model of the sizer is generated that allows analysis of product size distribution, wear and throughput. (C) 2003 Elsevier Ltd. All rights reserved.