Magnetic drain plugs attract and hold ferrous metal particles that circulate through your lubrication or hydraulic system. The particles may be a result of the following conditions; The constant flaking effect of normal wear of moving parts; Particles not removed by flushing after boring or machining; Chipping due to sub surface casting flaws; Minute component breakdown caused by stress usage.Usually it is a combination of factors that account for the presence of these particles that are abrasive and will cause excessive wear unless they are removed. Also an increase of material being collected on your magnetic plug may be an early warning of a potential problem.