It's normally a "U" shaped piece of Aluminum strip which fits round a large plastic bush, with a further flat section underneath to retain it. This rotates around the wing keel tube to allow roll control. Pitch is taken care of by the Hang Bolt which attaches the lower part of the U to the top of the Trikes Monopole. I would post a drawing or photo, but don't have any photo-hosting web site account.
P.S. if you want more details I could send some by Email....