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