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