A petroleum well drill- or coiled tubing string mounted fishing tool includes a main body including a lower housing with a magnet having at least one magnet surface facing downwards in the well at a lower end of the lower housing and arranged for catching and holding undesired magnetic objects present in the well, the main body provided with a connector to the drill- or coiled tubing string at its upper end. The tool further includes a generally cylindrical upper housing with a central channel with laterally directed curl flow forming nozzles through the cylindrical wall of the upper housing, the nozzles leading out into one or more helical grooves between helical ridges, the magnet including permanent magnets arranged in a magnetization pattern which concentrates their combined magnetic flux through the downwards facing surface, the upper housing's vertical channel extending near its lower end to peripherally directed channels extending to an outer wall of the lower housing about the magnets and leading to a
