Abstract: A rotary drill bit comprising a head and a roller cutter rotatably carried thereon, wherein an annular sealing means is arranged in an annular chamber adjacent to a gap between the roller cutter and the head. At least one of the sealing surfaces of the chamber is generally seen V-shaped. According to the invention larger sealing pressure is obtained at two circumferentially spaced portions of the V-shaped sealing surface than at an intermediate portion thereof while simultaneously maintaining sealing pressure along the entire circumferential extent of the sealing means between said spaced portions.