A magnetizer for a pipeline inspection tool. The magnetizer comprises a ferromagnetic base member, a pair of driving magnets mounted at spatially separate locations on the base member and a flux enhancing magnet mounted on the base member adjacent to one or both of the driving magnets. The directions of magnetization of the pair of driving magnets extend in opposite senses to each other, towards and away from the base member respectively to create a magnetic circuit that includes a flux path between the driving magnets which passes through the base member. The flux enhancing magnet has a direction of magnetization substantially aligned with the direction of magnetic flux on the flux path, the flux enhancing magnet being magnetically coupled to the adjacent driving magnets to drive flux around the magnetic circuit and thereby enhance the magnitude of a magnetic field exhibited by the magnetic circuit outside the magnetizer.