I took the oil filter off one of my engines and found this curious widget...

http://postimg.org/image/lzzrlmpu5/

It sits in the oil filter, has an impeller, is hollow and is magnetic (albeit weakly) at one end

http://postimg.org/image/etlz1kmdv/

http://postimg.org/image/ls79qbia1/

http://postimg.org/image/pqd3kzpj5/

I have never seen one before and it's not on the fische so I am guessing it's aftermarket?

I think it's a gadget supposed to collect any bits of metal from the engine and stop them getting into places you don't want them. Definitely seen one of these before. No idea if they really work though.