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