The small grooves 22, 23, 24 and 25 are close to {HEAD ~ rows} of {TAIL ~ V shaped grooves} 26, 27 and 28 and a set of spiral grooves 29 similar to those shown in FIG 2 
of
The small grooves 22 , 23 , 24 and 25 are close to { HEAD ~ rows } of { TAIL ~ V shaped grooves } 26 , 27 and 28 and a set of spiral grooves 29 similar to those shown in FIG 2
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH