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