Expressions are derived for the ploughing- (μ p), adhesion- (μ a) and total (μ) friction coefficients of spheres, cones and triangular- and square pyramids (with axis normal to the metal surface) ploughing along the surface of a metal. The effects of clogging of bonded abrasives such as emery paper by worn-off metal, and of pick-up of abrasive particles by the metal surface, are also considered quantitatively. Expressions are also developed for the wear mass M per unit distance, in terms of the maximum flow pressure ( p m ) and hardness ( H d ) of the metal, the abrasive particle shape, and either μ p or the total μ. The reciprocal of the volume wear rate ∞ h d . The linear ( M,μ) relation observed in practice at final equilibrium if pick-up is present, indicates that the fraction z.hfl ee of the load supported on emery/emery contacts is constant, independent of the emery particle diameter D. The data of avient, goddard and Wilman 2 for Al, Ag, Cu, Pt, Fe, Mo, U, and W, are discussed in the light of these theoretical expressions for μ and M. Estimates are obtained for z.hfl ee,μ p,μ a and s/ p m (where s = force/unit area to shear the abrasive/metal contacts). The friction coefficient μ ee of the emery/emery contacts is concluded to be ~1.