The rifle bolt threaded adapter stud is 5/16"-24 TPI to 10-24 TPI. You would need the thread adapter if replacing a factory fitted non-threaded fixed grip: Cut off the existing knob. Drill and tap a 10-24 TPI threaded hole into the bolt handle shank. Screw in the thread adapter. Then screw on any 5/16x24 threaded knob. (I have tactical bolt knob listed separately)