This is the right component if have a flat mount stock to be mounted to your Mac-10 .45/9mm SMG. This steel adapter slides into your existing wire stock slots and is secured by a button head bolt and a threaded internal block. Bolt, billet block and Allen head bolt (provided). The Rear of the adapter is flat with two threaded holes (10/32) for our Billet stock or an ACE type skeleton stock. You will need an AR 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) Installation instructions. *Fits Mac-10 SMG ONLYPlease call with questions, Weighs about 7 ounces.