{TAIL ~ A rolling cutter shell} is mounted upon the rotary head or {HEAD ~ the bit} for rotary motion to roll along the formations being cut 
{ TAIL ~ A rolling cutter shell } is mounted upon the rotary head or { HEAD ~ the bit } for rotary motion to roll along the formations being cut
TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH