This block combines the Hammer Drop Block and the Magazine Well Block into one unit. Not only does it provide a clamping point for the AR-15 lower, it also protects the hammer during dry fire. Inserts into magazine well and may be clamped in a vise to hold lower receiver in place during gunsmithing or maintenance. To use, remove upper receiver and place block in magazine well. Also allows dry-firing without hammer damage when installing or adjusting a trigger.