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 ... . This kind of bits cannot be used in broken or loose formatioSize Available:Q Series: AQ,BQ,NQ,HQ,PQ/AQTK ...