This listing is for a 4 pack of stainless steel automatic pig nipple drinkers.  ½" bite size with wrench body for easy wrench installation.  The stainless steel spring and dome provide long lasting protection from wear. Each nipple has a built in rear water filter mesh screen.  Attaches to standard 1/2 Inch NPT Pipe Threads.   This nipple drinker is ideal for sows and finishers.  The drinkers are of stainless steel, solid one piece construction.