{HEAD ~ The material} selected for {TAIL ~ the sheath} 18 may be the same as or different from the material chosen for the core tube 12, 
selected for
{ HEAD ~ The material } selected for { TAIL ~ the sheath } 18 may be the same as or different from the material chosen for the core tube 12 ,
HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH