The concept of a magnetic hydro-cyclone is undeveloped, possibly because studies by Bragard (1965) and the Royal School of Mines in London (Robinson, 1965) were not encouraging. Its role for the concentration of ironsands is attractive in that the classifying effect within a hydrocyclone may be comparable to the classifying effect in the gravity concentration of ironsands, and thus two steps may be achieved in one. Furthermore it should be a very simple and cheap process. The idea has been explored intermittently since 1976 but more energetically since the offering of a magnetic hydro-cyclone thickener by Boxmag Rapid (1983). This paper summarises the development and test work which are detailed elsewhere (Fricker, 1984).