The annular protrusion further has a distal end with {TAIL ~ an internal groove} with {HEAD ~ a base portion}, a front wall and a rear wall 
The annular protrusion further has a distal end with { TAIL ~ an internal groove } with { HEAD ~ a base portion } , a front wall and a rear wall
OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH