Replaceable cutting means substantially encircle {HEAD ~ the rolling cutter shell} for contacting the formations and forming {TAIL ~ a hole} therein 
for forming
Replaceable cutting means substantially encircle { HEAD ~ the rolling cutter shell } for contacting the formations and forming { TAIL ~ a hole } therein
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL OTH