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