Abstract: A magnetic tool for conditioning fluids includes a hollow core providing at least one passage through which the fluid to be treated flows. An array of magnets extends longitudinally along the core with the poles of the magnets arranged to provide a magnetic field perpendicular to the flow path to enhance the magnetic conditioning effect of the tool. The magnets are formed of a rare earth magnetic material, such as neodymium-iron-boron, and are backed by a flux-carrying member of cobalt-iron-alloy, with rounded corners to reduce loss of a magnetic field. Each magnet is mounted at least partially within an outer surface of the core with the flux-carrying member contacting, covering, and extending between the outer major faces of the magnets.