Surface set diamond core bits 1. Q Series: AQ,BQ,NQ,HQ,PQ ... : T2 46,T2 56,T2 66,T2 76 Surface set diamond core bits can be used with any type of core ... barrels. By varying the diamond grade,size,quality,and matrix hardness and crown shapes,the ... avoid excessive matrix wear at the leading edge of each segment,tungsten carbide inserts are fitted on each side of the ...