The cutting edges of {HEAD ~ the reamer sections} are parallel straight cutting edges or {TAIL ~ helical cutting edges} 
The cutting edges of { HEAD ~ the reamer sections } are parallel straight cutting edges or { TAIL ~ helical cutting edges }
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL