A system 2, wherein said {TAIL ~ drilling rotary blades} of {HEAD ~ said drilling} means are caused to move by impact in rotation 
A system 2 , wherein said { TAIL ~ drilling rotary blades } of { HEAD ~ said drilling } means are caused to move by impact in rotation
OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH