IADC Classification Nomenclature for Tooth and
The numbers 4, 5, 6, 7 and 8 are tungsten carbide inserts designed for different hardness with 4 being softest and 8 being the hardest. The second digit indicates formation hardness the bit was designed to drill. The number 1 is the softest formation and 4 the hardest. The third digit indicates bearing type.
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