each of said sockets has a cam member contained in the other of {HEAD ~ said pair} of {TAIL ~ holes}, and 
each of said sockets has a cam member contained in the other of { HEAD ~ said pair } of { TAIL ~ holes } , and
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH