Breather, Filter, Black/Chrome
These very populare oil breather filters can be used to help vent off any excess oil pressure in your engine case, and hence help to reduce oil leaks from your engine.
It is not intended for any specific fitment, but can be used wherever you see fit, on your oil installation.
Many people use these directly on a standard, or aftermarket oil filler neck, to replace the original hose that simply vented out through the engine tinwear. It's a more attractive solution.
Note though, that if intend using it on standard filler neck, it would clash with the late model 'plastic' style oil filler caps, no problem with metal caps though.