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 {TAIL ~ the outer surface} of the section 
over
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 { TAIL ~ the outer surface } of the section
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 HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH