{TAIL ~ The propped block} 31 is formed with spaced horizontal propped surfaces 312, and 313 at {HEAD ~ different heights} 
{ TAIL ~ The propped block } 31 is formed with spaced horizontal propped surfaces 312 , and 313 at { HEAD ~ different heights }
TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD