... 8 1/2" Steel Tricone Drill Bits 1-API or ISO 9001:2008 2-Delivery Date: In 7 days 3-Delivery term: By sea/air ... with high durability and maximum penetration rates. 2,Soft to medium formations(121,124,126, ... and other formations with intermittent hard streaks. 3,Medium to hard formations(213,214,215, ... 617G12 1/4311.1437G, 517G, 537G, 617G, 627G, 637G17 1/2444.5517G, 537G, 617G, 627G, 637G API 8 1/2" steel ...