I use .004" on all my tubes, some will say thicker latex runs easier and doesn't lose its tension, I really can't say because with my newest tube the GULP it has three orings on it, there is noway to have it slip once it is installed and if you want more raspiness then take off the top one or top two orings and it is there. I also was shown a trick to increase the raspiness on a single oring setup and that was to knick just to the inside of the inside diameter on the tube above the lip rest on either side...