Here, from DesktopAviator.com is a 4 inch diameter Trim Wheel with .25in center hole. It was designed to emulating the original Cessna Trim Wheel found in the 172 ect aircraft. For more DTA items stop by for a look at all of our extensive collection Flight Simulator Circuit Boards and Panel.
The Trim Wheel is an stl file. It can be printed using any standard 3d printer (we used the da Vinci mini). It takes about 1 hour for each half to be printed. With a .25 inch center hole, the TW can be easily mounted on a 100K ohm linear potentiometer