said groove being inclined at an inclination angle π−α with {TAIL ~ respect} to {HEAD ~ said coupling direction} 
said groove being inclined at an inclination angle π−α with { TAIL ~ respect } to { HEAD ~ said coupling direction }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD