The Shorty Stock by Q is compatible with mil-spec AR/M4 receiver sets and bolt carrier groups. Tools Needed: TORQUE WRENCH CAPABLE OF 35 FT-LB 3/4 " DRIVE SOCKET BLUE LOCTITE THICC ALLEN KEY MAG-WELL VICE BLOCK BENCH VISE Parts Include: STOCK RECOIL SPRING 5.56/300 BUFFER (3 oz) ASSEMBLEY TOOL Specs: WEIGHT: 14.5 oz W/ SPRING AND BUFFER COLOR: GRAY OR BLACK 2-POSITION