{HEAD ~ The main port} is {TAIL ~ a large central recess} 9 through which the belts of continuous grinding belts can be changed 
is
{ HEAD ~ The main port } is { TAIL ~ a large central recess } 9 through which the belts of continuous grinding belts can be changed
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH