In a magnet assembly (1), as is used for measuring rotation angles and torques for example, a magnetic plastic part (2) is connected to a metallic support sleeve (3) in such a way that the plastic part bears directly on flange elements (5, 6) of the support sleeve (3), and in such a way that protuberances (10, 11) of the plastic part produce a form-fit connection between plastic part and support sleeve, which connects these in the direction of the common central longitudinal axis of plastic part and support sleeve. The form-fit connection can be inherently non-releasable and thus permanent, or additional blocking means can be provided which prevent release of the form-fit connection.