The famous Hardbar Delrin shift knobs are CNC machined from solid genuine DuPont Delrin. Unlike aluminum or titanium knobs, the Delrin is great in that it does not burn your hand in the Summer heat, nor does it seem cold in the Winter. They are made for each application and do not use inadequate set screws that can and do loosen like the one-size-fits-all generic knobs. The C4/C5 knobs are fully threaded internally, whereas the C6 knobs are made specifically for the C6/C6ZO6 and use the stock Torx head screw in the machined counterbore. They are easily installed and easily removable. C6 shown.