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