two of {HEAD ~ said plates} are insertable in {TAIL ~ opposite directions} into said entrances, respectively, in said flat sleeve 
two of { HEAD ~ said plates } are insertable in { TAIL ~ opposite directions } into said entrances , respectively , in said flat sleeve
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH