... compressive strength strength and high drillability,such as soft shale,clay and salt bed,etcHardfaced gage and all tooth surfaces. ... compressive strength strength and high drillability,such as soft shale,clay and salt bed,etcHardfaced gage and all tooth surfaces, ... with low compressive strength and high drillability,such as shale,clay,sandstone and soft limestone,etc.Large radius offset crested scoop ...