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