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Roller cone bit classification

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Roller-cone bits are generally classified as either tungsten carbide insert (TCI) bits or milled-tooth bits. To assist in comparison of similar products from various manufacturers, the International Association of Drilling Contractors (IADC) has established a unified bit classification system for the naming of drill bits.

IADC roller-cone bit classification method

The IADC Roller-Cone Bit Classification Method is an industry-wide standard for the description of milled-tooth and insert-type roller-cone bits. This coding system is based on key design- and application-related criteria. The currently used version was introduced in 1992 and incorporates criteria cooperatively developed by drill bit manufacturers under the auspices of the Society of Petroleum Engineers [1].

IADC classification

The IADC classification system is a four-character design- and application-related code. The first three characters are always numeric; the last character is always alphabetic. The first digit refers to bit series, the second to bit type, the third to bearings and gauge arrangement, and the fourth (alphabetic) character to bit features.


Series, the first character in the IADC system, defines general formation characteristics and divides milled-tooth and insert-type bits. Eight series or categories are used to describe roller-cone rock bits. Series 1 through 3 apply to milled-tooth bits; series 4 through 8 apply to insert-type bits. The higher the series number is, the harder or more abrasive the rock type is. Series 1 represents the softest (easiest drilling applications) for milled-tooth bits; series 3 represents the hardest and most abrasive applications for milled-tooth bits. Series 4 represents the softest (easiest drilling applications) for insert-type bits, and series 8 represents very hard and abrasive applications for insert-type bits.

Unfortunately, rock hardness is not clearly defined by the IADC system. The meanings of “hard” sandstone or “medium-soft” shale, for example, are subjective and open to a degree of interpretation. Thus, information should be used only in a descriptive sense; actual rock hardness will vary considerably, depending on such factors as depth, overbalance pressure, porosity, and others that are difficult to quantify.


The second character in the IADC categorization system represents bit type, insert or milled tooth, and describes a degree of formation hardness. Type ranges from 1 through 4.

Bearing design and gauge protection

The third IADC character defines both bearing design and gauge protection. IADC defined seven categories of bearing design and gauge protection:

  1. nonsealed roller bearing (also known as open bearing bits)
  2. air-cooled roller bearing (designed for air, foam, or mist drilling applications)
  3. nonsealed roller bearing, gauge protected
  4. sealed roller bearing
  5. sealed roller bearing, gauge protected
  6. sealed friction bearing
  7. sealed friction bearing, gauge protected. Note that “gauge protected” indicates only that a bit has some feature that protects or enhances bit gauge. It does not specify the nature of the feature. As examples, it could indicate special inserts positioned in the heel row location (side of the cone) or diamond-enhanced inserts on the gauge row.

Included features

The fourth character used in the system defines features available. IADC considers this category optional. This alphabetic character is not always recorded on bit records but is commonly used within bit manufacturers’ catalogs and brochures. IADC categorization assigns and defines 16 identifying features.

Only one alphabetic feature character can be used under IADC rules. Bit designs, however, often combine several of these features. In these cases, the most significant feature is usually listed.


  1. McGehee, D.Y., Dahlem, J.S., Gieck, J.C. et al. 1992. The IADC Roller Bit Classification System. Presented at the SPE/IADC Drilling Conference, New Orleans, Louisiana, 18-21 February. SPE-23937-MS.

Noteworthy papers in OnePetro

Parys, P.G., Langford, J.W., and Berga, P.K. 1997. Improved Roller Cone Bit Selection Through the Use of an Attribute Based Bit Classification System, SPE/IADC Drilling Conference, 4-6 March 1997, Amsterdam, Netherlands, 37582-MS,

External links

International Association of Drilling Contractors

See also

Roller cone bit design


Page champions

Sebastian Desmette