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