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