If I'm not mistaken you have a boat with spade rudder?I have a C&C 35 Mk II, which had an Edson steering pedestal and wheel and which I removed, as I prefer a tiller. It has an emergency tiller which fits over a "rudder head" at the back of the cockpit (see picture here: https://www.dropbox.com/sc/w8irjonv0zojfkz/AADWiDICiqmBFsjtjzi2oEQra).
But is this really the rudder head? The emergency tiller fits over the 1-1/8" stainless cube, which becomes a threaded cylinder. The cylinder appears to be screwed into a bronze collar.
But is that right? Or is the stainless cube really the rudder head with a bronze collar fitter over it?
I would really like to buy or fabricate the piece to hold the tiller, but I can't quite figure out what I'm looking at. Any help would be greatly appreciated!
The bronze collar is most probably preventing the rudder from falling out of the boat.
The square top is the top of the rudder post (or shaft), this is the normal way to rig emergency steering on a wheel steered boat.