My desk has a 1 5/8" thick top, which the clamp accommodates. If your top is of a different dimension, use a longer or shorter bolt to fit your needs. This system allows for quick attachment or removal of your wheel, while tightly securing it to your desk without worrying. In the illustration at right, you can see how the tightening knob works. These can be found in some hardware departments, but you can also construct them yourself from two pieces of wood, plastic, or other dense material. Basically, it's two disks about 3/8" thick; one has a 1/4" hole in the center, the other is cut out to accommodate the hex head. Glue them together and slip the bolt through the knob, so the hex part of the bolt fits snugly into the cutout. The knob acts as a wrench of sorts, while tightening the bolt into the Tee-Nut. 

An even simpler solution to this would be a radio knob fitted with a set screw. Just cut off the hexhead end of the bolt and file a flat side on the shaft. This will accept the setscrew, and prevent the knob from slipping. I've seen some in Radio Shack that would do the trick. Although slightly smaller in diameter (aprox. 1"), it would provide you with enough torque to secure the wheel down tightly.