... hard; sampling drilling, tunnel drilling and shallow engineering drilling. AQ,BQ,BQ3,NQ,HQPQ,PQ3Double tube impregnated diamond core bitΦ46,Φ56 ... 275,Φ3251. Drilling for the hardness and abrasiveness complete strata.2. The strata of ractured congested the core of double ... Small diameter and shallow drilling in project. AQ,BQ,BQ3,NQ,HQPQ,PQ3Double tube electroplated diamond core bit and reaming shell ...