Midwest upper receiver rod works with any standard M4/M16 barrel extension and is excellent for removing stubborn or seized barrel nuts without damaging the upper. It is designed for muzzle device installs and can be used to install forward assist/port door covers. It can be installed horizontally or vertically in a bench vise. *Not compatible with 9mm/rimfire barrels, DPMS G2 308, Sig MCX Virtus/Rattler.