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