Update:

If you like this knob, I suggest that you go to http://www.thingiverse.com/thing:54024 and open it in the customizer. It will let you make this knob and many others in exactly the dimentions you want.

This is basic knob. It is slightly tapered. It has a divot at the top which you can paint with enamel paint if you wish. If you have several knobs on a device you could dsitinguish them by the color of this paint.

The hole for the shaft is 5.9mm diameter and 5mm deep. There is a hole on the side for an M3 set-screw if necessary.