IADC Tricone Bit Code Chart — How to Choose

What the IADC Bit Code Means

The IADC code is a classification system created by the International Association of Drilling Contractors so that roller-cone (tricone) bits from different manufacturers can be compared on a common scale. Because every maker uses its own product names and internal part numbers, two bits that look very different on paper may actually be intended for the same rock. The IADC code strips away the branding and describes each bit with a standardised three-character code — usually written as three digits, sometimes with an optional fourth letter for extra features — that tells you the formation class, the relative hardness within that class, and the bearing and gauge design.

The first digit identifies the series, which combines cutting-structure type with broad formation hardness. Digits 1–3 are milled-tooth (steel-tooth) bits for soft to hard formations, while digits 4–8 are tungsten-carbide-insert (TCI) bits running from soft all the way through to extremely hard, abrasive rock. As the first digit climbs, the formation gets harder and the cutting structure gets shorter and more durable.

The second digit subdivides hardness within that series on a scale of 1 to 4, where 1 is the softest rock the series targets and 4 is the hardest. So a 1-1 bit is for the very softest ground in the milled-tooth range, while a 1-4 bit is for the harder end of that same milled-tooth band.

The third digit describes the bearing and gauge design, and this is where IADC packs the mechanical detail: 1 = standard (open) roller bearing; 2 = air-cooled roller bearing; 3 = gauge-protected roller bearing; 4 = sealed roller bearing; 5 = sealed roller bearing with gauge protection; 6 = sealed friction (journal) bearing; 7 = sealed friction bearing with gauge protection; 8 = directional; and 9 = other or special features. An optional fourth letter (for example, a code suffix for enhanced cutting structure, motor applications or special seals) captures features the three digits cannot.

Put it together with a worked example: an IADC 5-3-7 is a TCI bit (first digit 5, soft-to-medium insert series) for a medium-hard formation (second digit 3) built with a sealed friction bearing and gauge protection (third digit 7). That single code tells a driller more about fit-for-purpose than a glossy product name ever could.

Milled-Tooth vs TCI: Choosing the Cutting Structure

Milled-tooth (steel-tooth) bits have long teeth machined directly from the cone steel and then hardfaced with a wear-resistant overlay. The teeth are tall and aggressive, which gives high rate of penetration (ROP) and a lower purchase price, and they shine in soft, sticky or non-abrasive formations where a long tooth can take a big bite of rock. The trade-off is wear: in hard or abrasive ground the steel teeth round off quickly and the bit loses its cutting profile.

TCI (tungsten-carbide-insert) bits replace machined teeth with pressed-in tungsten-carbide buttons. Carbide is far harder and more abrasion-resistant than hardfaced steel, so TCI bits last much longer in hard and abrasive rock — at a higher cost per bit. The button shape tracks formation hardness: long chisel-shaped inserts are used in softer rock where penetration matters, and short conical or hemispherical inserts are used in hard rock where the insert must resist breakage and abrasion rather than gouge deeply.

This is exactly what the IADC first digit encodes: 1–3 are milled-tooth, 4–8 are TCI. In Indian operations the choice is very real. Milled-tooth bits remain common for the soft, sticky Cambay shale in the top-hole section of Gujarat wells, where their aggressive bite and low cost suit the formation. TCI is essential when the bit reaches hard Deccan basalt or the abrasive sandstones of the Gondwana sequence, where milled teeth would be destroyed in a fraction of the footage.

Mapping IADC Codes to Volgaburmash Series

Once you can read an IADC code, the next step is matching it to a product family. The table below maps common IADC ranges to the Volgaburmash tricone series VBM India supplies, with the formation type and cutting structure each range targets.

The third digit — the bearing choice — deserves its own thought for Indian wells. For deep, high-temperature wells where bit life on bottom is paramount, sealed friction (journal) bearings (third digit 6 or 7) hold up far better than open roller bearings, which is why hot deep wells usually call for x-x-6 or x-x-7 codes. For directional and motor-driven sections — common in the Cambay basin and offshore Krishna-Godavari (KG) wells — motor-rated codes and the Motor / MotorPro series keep the bearing and cutting structure matched to the higher RPM and side loads a downhole motor imposes.

IADC Codes for Indian Formations

Indian basins span an unusually wide hardness range, so the IADC code that fits one section can be wrong a few hundred metres deeper. Three concrete examples show how the code maps to real ground:

• Cambay shale (Gujarat, Cambay basin) — soft to medium and notoriously sticky. Milled-tooth bits in the IADC 1-3-x to 3-2-x range from the Grand (GRD) series suit it well. Because the shale tends to ball up on the cones, choose designs with larger junk slots and plan hydraulics to keep the bit clean.
• Deccan basalt (Maharashtra, Madhya Pradesh and parts of the Gujarat traps) — very hard and abrasive. This is TCI territory, typically IADC 7-3-x to 8-2-x from the GrandXtreme series, with short conical inserts to resist breakage and a sealed friction bearing for long bit life in punishing rock.
• Gondwana coal-measure sandstone (Damodar valley, Son-Mahanadi belt; common in coal exploration) — medium-hard and abrasive. TCI bits around IADC 5-2-x to 6-3-x from the GrandPro series are a sound fit, and gauge protection is important because the abrasive sandstone wears the bit's outer row and can undersize the hole.

Public-sector tenders from ONGC and Oil India routinely specify bits by IADC code alongside API Spec 7-1 connection and rotary-shouldered-connection requirements, so quoting the right code is part of being compliant, not just technically correct. Buyers are also price-aware in a sophisticated way: experienced drilling engineers compare cost-per-metre across offset runs, not just the headline bit price, because a cheaper bit that dulls early can be far more expensive once rig time and trip costs are counted.

Beyond the Code: Picking the Right Bit

The IADC code is a starting point, not a full specification. It deliberately compresses a complex bit into three characters, which means it does not capture several things that decide success on bottom: the hydraulic configuration and nozzle (TFA) selection, the exact tungsten-carbide insert grade, the precise gauge geometry, or the dull-grade history from offset wells. Two bits sharing the same IADC code can perform very differently once these details diverge.

So treat the code as the filter that narrows the field, then refine the choice with real data. Pull the offset bit records and dull grades from nearby wells to see what actually worked and why bits came out. Match the nozzle total flow area to your available flow rate and standpipe pressure so the cones stay clean and cuttings clear the face. Decide between rotary and motor drilling, since that changes both the bearing code and the cutting-structure aggressiveness you want. And when in doubt, talk to the VBM India engineering team, who can read your formation tops and offset data against the Volgaburmash range. The goal throughout is the same metric the best operators optimise: the lowest cost-per-metre for the section, not the cheapest bit on the shelf.

See the full tricone bit range, compare with PDC bits, or read about DTH vs tricone for borewell drilling.