providing {HEAD ~ a cap} having a third lock element which mates with {TAIL ~ a fourth lock element} on said cylinder; and 
providing { HEAD ~ a cap } having a third lock element which mates with { TAIL ~ a fourth lock element } on said cylinder ; and
OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH