Here is a knurled knob for use with a RepRap Discount LCD controller. It makes use of the Knurled Surface LIbrary V 2 by aubenc for OpenSCAD.
This version includes a finger-sized dent for easy spinning.
It will also work with any other device that uses a 6mm D-shaft.
I recommend printing this part in ABS. Simply print, then shove onto the LCD controller shaft.