Common to {HEAD ~ all these arrangements} is {TAIL ~ the characteristic} that the working surfaces of any pair are converging and asymmetrical 
is
Common to { HEAD ~ all these arrangements } is { TAIL ~ the characteristic } that the working surfaces of any pair are converging and asymmetrical
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH