Drill rod: BQ, NQ, HQ , PQ , 1-BQ,NQ, HQ, ... internal and external surface casing shall not fold, hair grain, overburden bed separation grouting, crack, rolling fold and scarring. These defects ... thickness.(3) the surface not couplings have folded, hair grain, overburden bed separation grouting, crack, rolling fold, scarred and other ... 1000 Pieces/month Delivery Time within 7 work days Drill Rods