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