Midwest Industries Upper Receiver Rod & Barrel Extension Wrench for AR15/M4 The ultimate tool for barrel nut installs or removal without damaging your receiver. For use with AR15/M4 upper receivers, will not work with AR10s. Features: Designed for muzzle device installs and will not damage index pin Can be used to install forward assist/port door cover Compatible with forged and billet upper receivers Machined from 4140 Ordnance grade steel Durable Black Oxide finished for years of use Will not mar or damage exterior of upper receiver Receiver mounted sights can be left installed Can be installed horizontally or vertically in bench vise Works with any standard M4/M16 barrel extension 100% Made in USA Compatibility Notice Not compatible with 9mm and rimfire barrels Not Compatible with AR10s Not Compatible with Sig MCX / MCX Virtus / MCX Rattler