A drill bit latch assembly for releasably securing an earth drill bit to the bottom end of a drill string comprises a tubular housing adapted to be secured to the bottom end of a tubular drill string, drill bit holder adapted to be secured to a drill bit, and a latch assembly. The drill bit holder is...http://www.google.de/patents/US4860838?utm_source=gb-gplus-sharePatent US4860838 - Latching bit sub
