In order to grade the used bits, IADC published the Three Point Dull bit Grading Scheme.
为了对已使用的钻头进行磨损定级，IADC制定了T - B - G钻头磨损三位定级方法。
Because it cannot fully evaluate the dull bit characteristics, IADC published the Eight Point dull bit Grading scheme to replace the old scheme.
由于其不能全面反映钻头的磨损情况，后来又制定了钻头磨损八位定级方法。
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