a) said clamping lock housing and said {HEAD ~ central retaining element} are made of {TAIL ~ plastic} 
are made of
a ) said clamping lock housing and said { HEAD ~ central retaining element } are made of { TAIL ~ plastic }
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL