... strong hard; sampling drilling, tunnel drilling and shallow engineering drilling. AQ,BQ,BQ3,NQ,HQPQ,PQ3Double tube impregnated diamond core bitΦ46,Φ56,Φ59,Φ ... Small diameter and shallow drilling in project. AQ,BQ,BQ3,NQ,HQPQ,PQ3Double tube electroplated diamond core bit and reaming shellΦ46,Φ ... 56,Φ59,Φ66,Φ75,Φ76,Φ77,Φ91,Φ94,Φ110,Φ1301. Used for drilling weak ...