The 2 Stage Hook Under Trigger Set is designed for an easy drop in assembly in any mil-spec AR-15. It implements a self-centering patented disconnector for a smooth even 4.2-4.6 lb. trigger pull. All critical working parts are precision ground to ensure the highest accuracy. All parts are heat treated and case hardened by a Government approved facility. The 2 Stage Hook Under Trigger Set is designed for .154″ pins.