Because of the extreme flux densities of up to 5 Tesla, required to magnetise rare earth materials, currents in the conductors of magnetising tooling must be of the order of thousands of amps. The geometry of the magnet or assembly to be magnetised will dictate the maximum space available for these conductors, and so conductor sizes typically range from sub-millimetre to a few millimetres in diameter. The current densities present in these conductors cannot be sustained for more than a few milliseconds without overheating the conductor, damaging insulation, or ultimately fusing. Even in this short time period, the conductor temperature rise will be significant, and for most practical situations, a cooling strategy will be required. A single shot magnetisation process may raise the conductor temperature by over 100C. The heat removal rate when magnetising on a more frequent cycle, like an automated production situation, could be several kilowatts. Heat paths, materials and thermal stresses must all be considered, and much of the design process can be aided by the use of finite element modelling.