positioning said cap on said cylinder, and aligning said third lock element with {HEAD ~ said fourth lock element}, such that said third lock element mates with said fourth lock element to lock {TAIL ~ said cap} onto said cylinder 
positioning said cap on said cylinder , and aligning said third lock element with { HEAD ~ said fourth lock element } , such that said third lock element mates with said fourth lock element to lock { TAIL ~ said cap } onto said cylinder
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH