The Geissele AR15/M4 MIL-SPEC Buffer Tube Reaction Block 05-314 is built to solve a problem every armorer runs into eventually: torquing a castle nut down properly requires real force, and holding a lower receiver steady with one hand while working with the other usually means either an extra set of hands or a receiver finish that ends up scratched. Once the buffer tube is installed, the lower receiver slides directly into this Geissele Reaction Block at the 12, 3, 6, or 9 o'clock positions. That's the detail that sets it apart from a basic vise block: rotating the receiver 90 degrees at a time is as simple as loosening the provided nylon screws, pulling the lower out, and sliding it back in at the new orientation. No re-clamping, no repositioning the whole setup on the bench. Steel construction gives this Geissele Buffer tube tool the rigidity needed to handle serious torque without flexing or marring the receiver, while the nylon screws that secure the lower in place are soft enough not to damage the finish during repeated use. The result is an ultra-stable platform for a whole range of lower receiver operations, from installing the buffer retainer nut to general assembly work, all while keeping both of the armorer's hands free. For anyone doing regular AR-15 lower buffer work, whether professionally or on a home bench, this tool trades the usual frustration of one-handed assembly for something that actually holds still. Key Features Rotates the lower receiver at 12, 3, 6, and 9 o'clock positions Rotate in 90-degree increments by loosening the nylon screws Steel construction for handling serious torque Non-marring nylon screws protect the receiver finish Frees both hands for buffer tube and castle nut installation Simplifies buffer retainer nut installation Ultra-stable platform for a range of lower receiver operations Made in the USA Geissele Automatics Geissele AR15/M4 MIL-SPEC Buffer Tube Reaction Block 05-314