Peter,
It is just a round plug (to suit the bore of the steering column) with a threaded stud (about 3/8" long) in the top to suit the large chrome dome nut. From memory, when fitted, it stands about 1/2" proud of the top of the steering column (to suit the height of the cover plate around the handlebar links). If you make it an easy fit, you can Loctite it at the required height after fitting the tank and headlamp nascelle.
Regards,
Eddie.