Because {HEAD ~ the teeth} of the ratchet wheel are formed at {TAIL ~ the annular groove} around the periphery , the fabrication process of the ratchet wheel is complicated 
Because { HEAD ~ the teeth } of the ratchet wheel are formed at { TAIL ~ the annular groove } around the periphery , the fabrication process of the ratchet wheel is complicated
OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH