Got a knob from the hardware store that is formed out of heavy wires into an elongated football shape. Cut a slot in the base, drilled and tapped it for a cross screw and it will work fine and look relatively correct for the period in a steampunk sort of way. A 5/16 compression fitting worked nicely and I used a brake line fitting so I can use the flared connection on the brake line tubing. Maybe I will make a pair of sleeves with setscrews to anchor the wires. That would be a more positive retention method. The wire should be here monday and by then I may be ready to run the tractor.