The cutters include {TAIL ~ at least two concentric arrays} of {HEAD ~ primary preform polycrystalline diamond cutters} which are radially spaced so as to define an annular groove in the cutting profile, between the two arrays 
The cutters include { TAIL ~ at least two concentric arrays } of { HEAD ~ primary preform polycrystalline diamond cutters } which are radially spaced so as to define an annular groove in the cutting profile , between the two arrays
OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH