{HEAD ~ A propped block} 31 is joined to {TAIL ~ a lower side} of the connecting block 3 
is joined to
{ HEAD ~ A propped block } 31 is joined to { TAIL ~ a lower side } of the connecting block 3
HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH