The bottom surface of {HEAD ~ the mounting surface structure} attached to {TAIL ~ a top end} of the adjustable post mechanism 
attached to
The bottom surface of { HEAD ~ the mounting surface structure } attached to { TAIL ~ a top end } of the adjustable post mechanism
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH