{TAIL ~ The weakened zone} 22, which is located in the centre of tube section 20, is constituted by a thinner zone obtained by making {HEAD ~ an annular groove} over the outer surface of the section 
{ TAIL ~ The weakened zone } 22 , which is located in the centre of tube section 20 , is constituted by a thinner zone obtained by making { HEAD ~ an annular groove } over the outer surface of the section
TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH