The surface portion is substantially circular when viewed in a direction of the axis and is non parallel to the axis and including at least two contact points disposed at {HEAD ~ a lesser distance} from the axis than a region between {TAIL ~ the at least two contact points} 
The surface portion is substantially circular when viewed in a direction of the axis and is non parallel to the axis and including at least two contact points disposed at { HEAD ~ a lesser distance } from the axis than a region between { TAIL ~ the at least two contact points }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL