The Real Avid Lug-Lok Vise Block is an AR-15 upper-receiver work fixture that secures the upper by its barrel lugs rather than clamping the receiver exterior. The aluminum block slides through the upper and into the barrel extension's star chamber, so torque transfers to the steel lugs - not to the relatively thin aluminum receiver walls. Key features: Secures AR-15 uppers by the barrel lugs - no receiver-wall clamping Aircraft-grade aluminum, non-marring contact surfaces Adjustable vise pins to hold the upper at any working angle Lock knob holds working angle in place Eliminates the receiver-flex / racking issues common with clamp-style blocks Compatible with mil-spec AR-15 upper receivers What you get: 1x Real Avid Lug-Lok Vise Block Best for: Barrel installation/removal, free-float handguard swaps, gas block work, headspace checks - any AR-15 upper job that historically required clamping a receiver in a vise. Removes the risk of marring or deforming the upper while still giving you a rock-solid work platform.