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