The edges of {HEAD ~ the slots} are lined with upstanding flanges which are sharpened to form {TAIL ~ cutting edges} 
The edges of { HEAD ~ the slots } are lined with upstanding flanges which are sharpened to form { TAIL ~ cutting edges }
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL