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