... surfaces for steel tooth bit.2. Gauge Structure of this series tricone rock bit :Multiple gauge protection ... 6.Main AvailabilitySize Bit TypeIn.mm6152.4 4.7,517, 537, 617, 637 6 1/2 165.1437,517,537,617,6377 1/2190.5517, 5378 1 ... /2215.9437, 535,517, 537,617,6379 1 ... 8250.8517,53712 1/4311.1437, 517,535, 537,617,63717 1/2444.5517,535,537 Oil Rig Drill Bit