After {HEAD ~ application} of {TAIL ~ individual twists}, two elementary yarns are twisted together to form a strand 
After { HEAD ~ application } of { TAIL ~ individual twists } , two elementary yarns are twisted together to form a strand
OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH