What Is an IADC Tricone Bit Code?

An IADC code is a three-digit classification used to describe characteristics of a tricone drill bit.

In the VBM Drill Bits reference guide, the three digits are organized as follows:

The reference guide identifies the first digit as the bit series:

• 1–3: Steel tooth, from soft to hard
• 4–7: TCI, from soft to hard
• 8: Hardest TCI, where offered

The second digit identifies the sub-class within that series, progressing from 1 as the softest to 4 as the hardest.

The third digit identifies the bearing and gauge configuration. In the supplied reference chart, 7 represents a sealed journal bearing with gauge protection, and this configuration is used throughout the guide.

Example: Reading IADC 617

Take 617 as an example:

• 6 = TCI bit series
• 1 = first, or softer, sub-class within that series
• 7 = sealed journal bearing, gauge protected

The code therefore gives you more information than simply saying that a bit is a TCI tricone. It also identifies where that bit falls within the classification system used by the reference chart.

How the IADC Code Relates to Formation Hardness

The most useful part of an IADC classification chart is connecting the bit code to the formation being drilled.

The VBM reference chart groups ground conditions by approximate compressive strength ranges and lists the IADC codes associated with those conditions. The ranges are presented in kg/cm², MPa, and 1,000 psi.

The chart progresses from very soft ground through increasingly hard rock.

Very Soft Ground

The chart begins with materials such as:

• Topsoil
• Sand
• Peat
• Loose cinder
• Loess
• Soft coke coal

For these conditions, the reference specifically states “No tricone code — soft formation tooling.”

The listed strength is below 50 kg/cm², below 7 MPa, or below 1,000 psi.

Soft to Medium Formations: IADC 117–447

The next range includes formations such as sandy or clay ground, moraine, soft marl, loam, weak rubble, gypsum, wet clay shingle, and medium coal.

The reference chart associates this range with:

117, 127, 137, 147, 417, 427, 437, and 447

The listed formation strength is approximately:

• 40–300 kg/cm²
• 4–14 MPa
• Less than approximately 1–2 thousand psi

These codes cover both steel-tooth and TCI classifications within the range identified by the chart.

Medium Formations: IADC 217–447

For somewhat harder conditions, the chart lists formations including anthracite, clay siltstone, barite, soft limestone, rock salt, frozen sand, iron ore, tuff, anhydrite, apatite, dolomite, hematite, and ironstone.

The associated codes include:

217, 227, 237, 247, 417, and 427

The reference strength range is approximately:

• 200–450 kg/cm²
• 14–31 MPa
• 2–4 thousand psi

This illustrates why the first two digits matter. Different bit classifications can appear within overlapping formation ranges, so the IADC code should be considered together with the actual drilling conditions rather than as an isolated number.

Medium-Hard Formations: IADC 317–647

As formation strength increases, the reference chart moves into formations such as siliceous or sericitic-cemented siltstone, apatite-nepheline ore, weathered dunite, magnetite, marble, serpentinite, siderite, and phosphorite shale.

The listed codes include:

317, 327, 337, 347, 417, 427, 437, and 447

For the next harder grouping, laminated siltstone, dolomite, granodiorite, gabbro, pegmatite, basaltic lava, mica-quartz schist, gneiss, granite-gneiss, weathered diabase, and mineralized marble are associated with:

317, 327, 337, 347, 617, 627, 637, and 647

The corresponding strength range reaches approximately 550–950 kg/cm², or 48–65 MPa.

Hard Formations: IADC 517–747

The chart then moves into harder formations such as:

• Amphibole
• Gabbro
• Conglomerated igneous pebble
• Granite-diorite
• Oxidized ferruginous quartzite
• Alkaline dike rock

The associated codes are:

517, 527, 537, and 547

The listed formation strength is approximately 750–1,100 kg/cm², or 65–76 MPa.

For granite-porphyry, fine-grained granite, diorite, and fine-grained sandstone, the same group of codes appears, with the listed strength increasing to approximately 1,100–1,350 kg/cm², or 76–93 MPa.

Very Hard Formations: IADC 617–847

The higher-strength sections of the chart include formations such as:

• Ferruginous quartzite
• Hard magnetite and hematite-magnetite ore
• Compact garnet skarn
• Olivine basalt and andesite
• Dacite
• Diabase
• Magnetite quartzite
• Quartz porphyry
• Quartzite sandstone
• Jasperite
• Chert
• Jasperoid shale

The chart uses combinations of 617–647, 717–747, and eventually 817–847 classifications as the formation hardness increases.

At the upper end of the reference, 817, 827, 837, and 847 are listed for formations including basalt, diabase, very dense porphyrite, solid jasperite, quartzite, jasper, corundum ore, massive pyretic hornfels, and hematite ore.

The listed strength is greater than:

• 2,500 kg/cm²
• 172 MPa
• 36 thousand psi

This represents the hardest formation category shown in the supplied quick-reference chart.

IADC Code Quick Reference by Formation Range

Ranges and code groupings are based on the VBM Drill Bits quick-reference chart. Some formation-strength ranges overlap between categories, so the chart should be used as a selection reference rather than as a standalone bit specification.

Why Formation Matching Matters

An IADC code is useful because it gives drilling professionals a standardized way to discuss tricone bit characteristics. The VBM reference chart demonstrates this directly: individual IADC codes appear across different formation categories, while different code families become relevant as the formation changes from soft to hard.

For example, the chart moves from 117-series steel-tooth classifications in softer conditions toward 617-, 717-, and 817-series TCI classifications as the listed formation strength increases.

That progression makes the IADC code a useful starting point when evaluating a tricone drill bit for a particular formation.

Steel Tooth vs. TCI in the IADC Classification

One of the first things the IADC code tells you is the general bit series.

According to the supplied reference:

• Series 1–3 represent steel-tooth bits, ranging from soft to hard.
• Series 4–7 represent TCI bits, progressing from soft to hard.
• Series 8 represents the hardest TCI classification where offered.

This distinction is particularly useful when comparing tricone options for different formation conditions.

Steel-tooth and TCI classifications are not interchangeable labels in the chart. They represent different sections of the IADC classification system and should be evaluated against the formation being drilled.

For buyers and drilling contractors, understanding the series portion of the code provides an immediate indication of where a bit sits within the classification system.

How to Read an IADC Code in Three Steps

Step 1: Identify the Bit Series

Look at the first digit. This identifies the broad series and, according to the VBM reference, distinguishes steel-tooth classifications from TCI classifications.

Step 2: Identify the Sub-Class

Look at the second digit. The second digit indicates the sub-class within the series, with 1 representing the softest and 4 the hardest within that series.

Step 3: Identify the Bearing/Gauge Configuration

Look at the third digit. In the supplied reference guide, the third digit is 7, representing a sealed journal bearing with gauge protection.

This three-step approach makes an IADC code much easier to interpret when reviewing tricone drill bit options.

IADC Classification Is a Starting Point, Not the Entire Selection Process

The IADC code provides valuable classification information, but it should not be treated as the only factor in bit selection.

Formation type and hardness are central to the supplied reference chart, but actual bit selection may require additional application information that is not provided in this one-page guide.

That distinction is important when ordering or specifying a tricone drill bit. The IADC code should be matched to the drilling conditions and the specific bit requirements of the application rather than selected solely by code number.

If the formation or required bit configuration is unclear, providing the drilling conditions to a qualified drill-bit supplier can help narrow the available options.

Conclusion

Understanding IADC tricone bit classification makes it easier to interpret tricone bit specifications and connect bit classifications with formation conditions. By reading the three digits as series, sub-class, and bearing/gauge configuration, drilling professionals can use the classification system more effectively when evaluating bit options.

For formation-specific selection, use the IADC classification as a starting point and match it to the actual ground conditions and application requirements.