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