The attrition and breakage of particles has been examined in a cone cell which permits the clearance between a rotating blade and a wall to be varied between experiments. Breakage is considerable if the clearance between the blade and the wall is just under one particle diameter or about 1% - 2 particle diameters. This effect has been found for a number of absolute initial particle sizes and for two materials of entirely different structure namely a polycrystalline urea and catalyst beads. Breakage is not detectable if the clearance is less than 0.25 particle diameters or greater than 2.5 particle diameters. A pronounced minimum attrition rate is found at about 1.25 particle diameters. An explanation of such effects is offered in terms of the particle packing. The findings are of considerable significance for understanding how attrition occurs in processing equipment. Studies on well characterised alumina extrudates have been conducted in the annular shear cell used in previous work for IFPRI. The cell has the advantage that the stress, strain and strain rate applied to deforming bodies of particulate solids are known. The extrudates have been made in the different strengths and have known and reproducible structures. A range of normal stresses varying by over three orders of magnitude could be imposed on the deforming bed of particles. The less strong extrudate showed a progressive decrease in fine attrition product as the normal stress decreased which indicated a shift in dominant mode of breakage from fragmentation to abrasion, but each mechanism remained at every stress. Both photographic evidence and particle size distributions confirmed this behaviour. For the harder particles the photographic evidence was consistent with this behaviour but the particle size distributions were erratic; it is thought that there is some limitation to the use of the cell but this remains to be proved . It was also found that re-use of broken material in the cell may affect behaviour and further is necessary to establish whether the unification of breakage data may be achieved for the full stress range as it was previously over a more restricted range. The annular shear cell is of most practical use for systems with high ambient stresses.