Machined from pre-hardened, stainless steel bar stock, this shoulderless thread adapter permits muzzle devices to sit tighter against the barrel shoulder and maintain full thread joint strength. Adapter screws fully into muzzle device, giving it a more streamlined appearance when fitted onto the barrel and ensuring a more accurate alignment to bore. All threads are single point cut in same operation to tight UNEF Class-3 tolerances for perfect concentricity and alignment. Allows attachment of 5/8-24 muzzle devices to a 1/2-36 threaded barrel.
Big Book Catalog, Issue:67, Page:176
Big Book Catalog, Issue:68, Page:183