a groove on said insert wall positioned such that said extensions are capable of fitting into said groove when said {HEAD ~ insert body} is located within said {TAIL ~ sleeve member} 
is located within
a groove on said insert wall positioned such that said extensions are capable of fitting into said groove when said { HEAD ~ insert body } is located within said { TAIL ~ sleeve member }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL OTH TAIL TAIL TAIL TAIL TAIL TAIL