A tool for retrieving metal debris from a wellbore has a plurality of magnet assemblies spaced longitudinally along a tool body (10). Each magnet assembly has a magnet member (42), which forms a primary debris settling area (70). Each magnet member is protected by a magnet protector. A secondary debris settling area is formed between a magnet and an adjacent magnet protector to allow utilization of the residual magnetic force created by the magnet members. The secondary settling area occupies at least half of the surface area of the primary settling area.