This is the right component if you want the feel and comfort of an AR stock on your MPA .45 acp gun. The adapter bolts to your gun and maintains a tight precision fit under rapid fire with the aid of a machined set screw underneath and a flat rear piece to mount any ace or flat mounted stock. The Rear is flat with two (10/32) threaded holes for our Billet stock or an ACE type skeleton stock. *Addition of this item may require additional paperwork to be filed with the ATF, check with your local dealers. This adapter fits ALL Master Piece Arms .45acp guns and rifles that have the threaded hole under the rear of the gun. You will need an AR FLAT MOUNT rear stock (our Billet tactical stock or an ACE skeleton stock) to complete the setup. Please see our section of REAR BUTT STOCKS (gun and other accessories sold separately) Finished in Flat/Matte Black. **TELL US IN THE COMMENTS SECTION OF YOUR ORDER IF YOU HAVE AN OPEN BOLT MAC-10, WE NEED TO GIVE YOU A DIFFERENT BOLT AND INNER THREADED BLOCK.