Brownells new AR-15 Armorer's Wrench works with either encapsulated or peg-style barrel nuts.  The long handle ends with a carbine buttstock wrench that features four teeth that ensure full engagement of all four notches in an M4-style receiver extension nut for easy removal and installation.
 
Also includes a 1/2" square drive opening for torque wrench application, 5/8" and 3/4" slots to fit receiver A2 receiver extensions and flash suppressors.