Hejian ZhongCheng Drill Bit Manufacture Co.LTD.
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An eight point dull grading system has been established by the IADC to enable drillers and bit manufacturers evaluate the performance of a drill bit. This eight point system is described below and is used on both tricones and fixed cutter bits:

1. Inner Cutting Structure - Inner cutting structure wear is also noted by a number ranging from 0 to 8 with 0 being no wear and 8 being total wear.

2. Outer Cutting Structure - Outer cutting structure wear is also denoted by a number ranging from 0 to 8 with 0 being no wear and 8 being total wear.

3. Dull Characteristics - Dull characteristics enables the bit salesperson or driller to determine the overall, distinctive aspect of the dulled drill bit according to IADC standards as follows:

4. Location - Location describes where the damage is on the cone. N - Nose Row; M - Middle Row; G - Gauge Row; A - All Rows

Cone Number One contains the centermost cutting component. Cones two and three follow in a clockwise manner.

Nose row is the centermost cutting structure.

Gauge row is the outer most cutting structure.

5. Bearings/Seals - For open or roller bearing bits, bearing life is estimated on a scale of 0 to 8. Zero equals complete bearing intact, eight equals no bearing life left. "X" indicates fixed cutter.

If the drill bit has a sealed bearing, an "E" indicates the seals are effective or "F" is used to indicate failed seals.

For more information on tricone bearing types, click here.

6. Gauge - Gauge measures the amount of gauge wear a drill bit has suffered. 1=1/16" out of gauge; 2=1/8" out of gauge; 4=1/4" out of gauge.

7. Other Dull Characteristics - Any other dull grading characteristics should be noted here using the codes from #3.

8. Reason Pulled - The following codes are used to indicate the reason a bit was pulled from the hole: