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