Jet JAS-14 1/4-Inch Threaded Pnuematic Swivel Coupler
This air swivel is a bidirectional 360 degree rotation air hose universal joint and is great accessory to keep your air hose straight and untwisted.  It increases the maneuverability of the tool and decreases operator fatigue.  For use with drills, grinders, screwdrivers, sanders, nailers, staplers, impact wrenches, etc.