The magnetizer oil filler cap houses a strong magnet to pick up the debris in the engine the oil filter misses. Oil filters have to be porous enough to flow oil through them quickly, so they can't catch all the metal.

The magnets pick up the metal the filters miss, and you'd be surprised how just how much they pick up. The best part is just remove the plugs and clean the magnets. You don't need to lose your oil anymore, like a magnetic drain plug, to clean off the magnet. This can be done between every ride or race.