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