said first and second openings having cross {HEAD ~ sectional configurations} of {TAIL ~ a type} to allow passage of said keeper element therethrough, 
said first and second openings having cross { HEAD ~ sectional configurations } of { TAIL ~ a type } to allow passage of said keeper element therethrough ,
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH