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