A magnetizer including a housing, a passage arranged inside the housing, and a permanent magnet assembly arranged outside the passage to provide a magnetic field passing through the passage. The housing defines an inlet to the passage and an outlet from the passage such that an object to be magnetised can be inserted into the passage via the inlet in the housing and removed via the outlet in the housing. The passage includes a uniform portion where opposing surfaces of the permanent magnet assembly are arranged a uniform distance apart along the length of the uniform portion and a diverging portion arranged between one end of the uniform portion of the passage and the outlet of the housing.