It's threaded so the steerer tube is slightly shorter than the head tube.
??????????????????? so how you gonna screw on top race, locking washer and locking nut [threaded headset components screwable (except washer:) on to the steerer tube thread] ?????????????
??????????????????? so how you gonna screw on top race, locking washer and locking nut [threaded headset components screwable (except washer:) on to the steerer tube thread] ?????????????