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