First, {HEAD ~ the unitary, shielded, perforate threaded collars} 42 are screwed onto {TAIL ~ the protruding threaded ends} 34 of the bolts and tightened to jam the nuts 40 against loosening 
First , { HEAD ~ the unitary , shielded , perforate threaded collars } 42 are screwed onto { TAIL ~ the protruding threaded ends } 34 of the bolts and tightened to jam the nuts 40 against loosening
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH