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By certification 
Drag bits also named blade bits, with a TC inserts on the blades.
They are usually designed for use in soft formations such as sand, clay, or some soft rock.Their uses include drilling water wells, mining, geothermal, environmental and exploration drilling.Whenever possible, they should be used to drill pilot holes, for they produce cuttings that are easiest to log.
They are usually designed for use in soft formations such as sand, clay, or some soft rock.Their uses include drilling water wells, mining, geothermal, environmental and exploration drilling.Whenever possible, they should be used to drill pilot holes, for they produce cuttings that are easiest to log.