{HEAD ~ A ratchet} allows {TAIL ~ the mill} to move toward the object relative to the mandrel and prevents the mill from moving away from the object relative to the mandrel 
allows
{ HEAD ~ A ratchet } allows { TAIL ~ the mill } to move toward the object relative to the mandrel and prevents the mill from moving away from the object relative to the mandrel
HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH