This breather is specially designed to screw into the oil cap hole on most late-model GM vehicles.  It allows the crankcase to vent if PCV has been disabled and has a nice finishing touch appearance. Made of billet aluminum instead of cheap plastic that can break or crack, comes complete with breather filter. Sold individually.

Breather now includes a check-valve inside

Do not use this breather with PCV system intact as this would create an intake leak.