I was fed up of the prusa original knob, so I made my own. In the original version I really didnt like the fact that if the extruded part of the knob was on the bottom, you really couldnt press the X button. Secondly, when choosing the file for printing, the software would sometimes think that you wanted to print the next file down, even if you maybe moved the knob just a little it. This happened really often and I was really frustrated. I made this one symmetric, so  you can always press the X button, as well as there is a small groove on top, which forms this guide for your finger, thus the software does not make a mistake as often.