A side ridge line 13 of {HEAD ~ the blade portion} 12b forms {TAIL ~ a cutting edge} 
A side ridge line 13 of { HEAD ~ the blade portion } 12b forms { TAIL ~ a cutting edge }
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL