A gap is defined between each lobe, {HEAD ~ the gap} being defined at {TAIL ~ the radial outer edge} 
defined at
A gap is defined between each lobe , { HEAD ~ the gap } being defined at { TAIL ~ the radial outer edge }
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL