Patente US4304312 - Percussion drill bit having centrally projecting insert - Google PatentesB???squeda Im???genes Maps Play YouTube Noticias Gmail Drive M???s ??Iniciar sesi???n B???squeda avanzada de patentesPatentesA percussion drill bit comprises a bit body including a shaft having a conical mounting portion to be mated with a conical mounting portion of a drill rod by means of substantially l