of the stripper rubber 16 due to a blow out which can rip and tear the rubber and thus cause failure of the seal the interior portion 20i located in the nose n of the stripper rubber provides a seal against the well bore component or kelly 15 but surfaces 20e 20f 20g and 20h do not provide a seal in the embodiment illustrated the overall diameter of the outside portion 20a of the stripper rubber 16 is 15 inches and the inner diameter of the cylindrical interior portion 20i is 4 125 inches the overall height that is the distance from the top annular rim 20d to the bottom annular rim 20c is about 10 14 inches for a stripper rubber of this size and similar sizes the convex knee component 20f has a 0 75 inch radius when the well bore component 15 is inserted into the stripper rubber 16 the convex component knee 20f serves as a bumper for centering the component 15 when larger components 15 are being pushed through the stripper rubber 16 the convex knee component 20f initiates the additional stretching process required to accommodate these larger diameter areas of the components 15 when drilling with high pressure in the bowl housing 10 of the rotating control head the convex knee component 20f provides additional rubber strength and mass as represented in cross sectioned area in the throat area t of the stripper rubber and under high pressure drilling or 34 kick 34 pressure surges the presence of the knee component 20f serves to limit the travel of the throat section t before it comes to bear against the drill pipe or other component this reduces the tendency of the stripper rubber 16 to blow out under extremely.