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