mounting fixtures configured to mount said device on {HEAD ~ a head} of {TAIL ~ said first user}, 
of
mounting fixtures configured to mount said device on { HEAD ~ a head } of { TAIL ~ said first user } ,
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH