Preferably, {HEAD ~ the projection} extends inwardly of the structure and is of {TAIL ~ circular cross section} 
Preferably , { HEAD ~ the projection } extends inwardly of the structure and is of { TAIL ~ circular cross section }
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL