An apparatus 4, wherein said pocket inner surface of {HEAD ~ said retainer} is formed into a shape which substantially coincides with the shape of the ball in contact with {TAIL ~ said pocket inner surface} at the major axis position of said cam 
An apparatus 4 , wherein said pocket inner surface of { HEAD ~ said retainer } is formed into a shape which substantially coincides with the shape of the ball in contact with { TAIL ~ said pocket inner surface } at the major axis position of said cam
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH