to aid in extraction of the cutting head 24 from the hard substrate for the invention as set forth in the embodiments shown in fig1 15 the teeth 44 may also be provided with additional material so that each tooth is wider than the thickness of the side walls of the hollow cylindrical body 20 one preferred hollow cylindrical body embodiment comprises an upper section 50 and lower section 52 wherein the lower section 52 defines a greater exterior diameter than the upper section 50 to facilitate removal of the cutting head 24 from the posthole and reduce or prevent binding during the drilling process moreover a hole slot slit or other opening 51 is optionally cut or formed into the upper section 50 to allow water to exit the head during the cutting operation and avoid causing a suction making removal of the rock plug difficult the flightless auger 10 is designed for interchangeable use with a conventional flighted auger used for removal soil from the post holes the quick disconnect feature of the flightless auger 10 makes the interchangeable augers practical to use together without wasting time upon hitting a hard substrate such as a rock ledge the flighted auger can be disengaged in minutes and the flightless rock auger 10 attached to the drilling rig the flightless auger 10 is lowered and raised with the hydraulic boom so that only the weight of the auger 10 exerts pressure on the rock substrate defining floating pressure although.