a ring gear of the reduction gear is screwed into {HEAD ~ an inner peripheral surface} of {TAIL ~ the first housing} through the first housing opening, wherein 
of
a ring gear of the reduction gear is screwed into { HEAD ~ an inner peripheral surface } of { TAIL ~ the first housing } through the first housing opening , wherein
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH