The wrench is the same as is included with the Knight's Armament URX 4 IBN handguards. It is normally used for installation or removal of the handguard.
Wrench is made for 1/2" ratchet/torque wrench. Round plastic buffer is removable. Removing the buffer allows the wrench to fit most URX 2/3.1 rails and can be used to aid in disassembly when the barrel nut or rail is stuck. Use with caution.