These Titanium "D" size adapters feature spanner wrench holes on the top face and are .1" thick protruding from the mounting face. Titanium “D” mounts have an external thread of 1-7/16×20 (1.4375x20). SDTA MBTA is for our Gen 1 muzzle devices that feature a coarse acme thread. The SDTA MBTA is not compatible with our Tapered line of muzzle devices.