8 1/2" Steel Tricone Drill Bits 1-API or ISO 9001:2008 2-Delivery Date: In 7 days 3-Delivery term: By ... ,134,136,137)These bits are designed to drill formations such as shales, medium soft limestone, ... ,214,215,217)These bits are designed to drill formations such as hard sandstone, dolomite, and ... , 617G12 1/4311.1437G, 517G, 537G, 617G, 627G, 637G17 1/2444.5517G, 537G, 617G, 627G, 637G API 8 1/2" steel ...