The CFS-HD classifier uses a combination of the free vortex and the forced vortex models to achieve cut points down to less than 2 mu m. The classifier rotor has a new design for theoretically constant radial velocity in the vane-free internal area; it is surrounded by a cage of static vanes, creating a steep spiral flow in order to give good dispersion and deagglomeration to the material to be classified. Cut points obtained from experiments are compared with a modified classifier equation, showing a linear relation even in the very fine range. The efficiency of the classifier is evaluated by means of Tromp＇s kappa-values and fines-yields, (Cut point and kappa-value are related to the Tromb curve, which is derived from the mass balance and the particle size distributions of coarse and feed fraction of a classification: T(d) = g . q(g)(d)/q(A)(d). The cut point is then defined as d(50)-value of the Tromb curve; the kappa-value is formed as quotient of the d(25) and the d(75) value: kappa = d(25)/d(75).)