{TAIL ~ The material} of which {HEAD ~ the covers} 30 are formed should have the same characteristics mentioned above in connection with the embodiment of FIGS 1 and 2 and should be slightly stressed when secured in place 
of are formed
{ TAIL ~ The material } of which { HEAD ~ the covers } 30 are formed should have the same characteristics mentioned above in connection with the embodiment of FIGS 1 and 2 and should be slightly stressed when secured in place
TAIL TAIL TAIL TAIL TAIL TAIL REL OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH