Tricone Bit University: How to Read an IADC Tricone Bit Code

When selecting a tricone bit, you may see codes such as IADC 517, 537, 637, 725, or 745.

But what does an IADC code actually tell you?

For drilling contractors and engineers, the IADC classification is more than a three-digit number. It provides a standardized way to describe the cutting structure, formation suitability, and bearing/seal configuration of a tricone bit.

In this edition of Tricone Bit University, we will break down the IADC code step by step.

1. What Is an IADC Code?

IADC stands for the International Association of Drilling Contractors.

The IADC bit classification system is widely used to categorize roller-cone drill bits according to their:

• Cutting structure

• Formation application

• Bearing/seal configuration

A typical IADC code consists of three digits:

IADC 6 – 3 – 7

Each digit provides different information.

The basic structure

So, when you see IADC 637, you should not read it as one number.

You should read it as:

6 + 3 + 7

Each digit has a specific meaning.

2. The First Digit — Cutting Structure & Formation Hardness

The first digit identifies the general cutting structure and the formation hardness range for which the bit is designed.

For TCI bits, the first digit generally falls within the 4–8 series.

Common TCI series

For example:

IADC 517

The first digit is 5.

This indicates a TCI bit designed for medium-soft formation applications.

IADC 637

The first digit is 6.

This indicates a TCI bit designed for medium-hard formations.

IADC 745

The first digit is 7.

This indicates a TCI bit designed for hard formation applications.

However, the first digit should never be used alone to select a bit.

Formation strength, abrasiveness, fracturing, drilling parameters, and hydraulic conditions all need to be considered.

3. The Second Digit — Formation Sub-Classification

The second digit further divides the formation range within the first-digit series.

For example, two bits may both belong to the 6-series but have different second digits.

This allows the classification system to distinguish between different formation conditions within the same general hardness range.

For example:

IADC 627
IADC 637
IADC 647

All three belong to the 6-series, but they are intended for different formation conditions within that general range.

This is important because "hard rock" is not a single drilling condition.

A formation can be:

• Hard but relatively non-abrasive

• Hard and highly abrasive

• Fractured

• Interbedded

• Highly variable

• Competent and massive

The correct bit therefore depends on more than simply asking:

"Is the rock hard?"

The drilling environment matters.

4. The Third Digit — Bearing and Seal Configuration

The third digit describes the bearing and seal system.

This is particularly important when comparing bits for demanding applications.

Common third-digit classifications include:

For example:

IADC 637

The final digit is 7.

This indicates a sealed-bearing bit configuration.

IADC 745

The final digit is also 5.

This indicates a sealed-bearing configuration.

This is why two bits with different cutting structures can still have similar bearing-system classifications.

5. Let's Read an IADC Code Together

Let's take a common example:

IADC 637

Break it into three parts:

6 → Formation / cutting structure series

The bit belongs to the 6-series, generally associated with medium-hard formations.

3 → Formation sub-classification

The second digit provides a more specific formation classification within the 6-series.

7 → Bearing and seal configuration

The final digit identifies the bearing/seal arrangement.

So:

IADC 637 = 6 + 3 + 7

It is not simply "a 637 bit."

It is a standardized description of the bit's cutting structure, formation application, and bearing configuration.

6. IADC 725 vs. IADC 745 — Why the Difference Matters

Consider two bits:

IADC 725
IADC 745

Both are in the 7-series, so both are intended for hard formation applications.

But the second digit is different.

This means the two bits are classified for different formation conditions within the hard-formation range.

This distinction can become important when drilling:

• Fractured rock

• Fragmented formations

• Hard interbedded formations

• Abrasive formations

• Variable ground conditions

For example, simply choosing a bit because it has a higher "hardness number" is not a sufficient selection method.

The formation's fracture behavior and abrasiveness can be just as important as compressive strength.

7. IADC Code Is a Starting Point — Not the Complete Bit Specification

One of the most common mistakes is treating the IADC code as the complete description of a tricone bit.

It isn't.

Two bits can have the same IADC classification and still perform differently in the field.

Why?

Because actual bit performance also depends on engineering details such as:

Cutting structure

• Insert grade

• Insert shape

• Insert density

• Insert projection

• Row configuration

• Cone geometry

• Gauge protection

Bearing system

• Bearing design

• Seal design

• Lubrication system

• Bearing load capacity

• Shirttail protection

Hydraulics

• Nozzle configuration

• Nozzle size

• Jet velocity

• Air/water flow

• Hole cleaning efficiency

Manufacturing quality

• Cone accuracy

• Heat treatment

• Bearing manufacturing

• Thread accuracy

• Insert retention

• Surface protection

Therefore:

IADC classification tells you what the bit is designed for. It does not tell you everything about how the bit will perform.

8. IADC Code vs. Actual Drilling Conditions

A bit selection should always start with the formation and drilling conditions.

Before selecting a tricone bit, consider:

Formation

• Rock type

• Compressive strength

• Abrasiveness

• Fracturing

• Interbedding

• Weathering

Drilling parameters

• Weight on bit (WOB)

• Rotary speed (RPM)

• Air / water flow

• Hole diameter

• Hole depth

Operational requirements

• Required ROP

• Expected bit life

• Bearing life

• Gauge retention

• Total drilling cost

A bit that works well in one mine may not produce the same result in another mine—even when the hole diameter and IADC classification are identical.

9. A Simple Way to Read Any IADC Code

When you receive a tricone bit specification, use this three-step method:

Step 1 — Read the first digit

Ask:

What formation hardness range is this cutting structure designed for?

Step 2 — Read the second digit

Ask:

What formation condition within that range is the bit classified for?

Step 3 — Read the third digit

Ask:

What bearing and seal configuration does the bit use?

Then move beyond the IADC code and check the actual bit design.

10. Don't Select a Bit by IADC Code Alone

At Milalion, we recommend looking at the complete drilling application rather than selecting a bit based only on the IADC number.

For example, when evaluating a bit for a fractured or fragmented formation, we would consider:

Formation → Cutting Structure → Bearing System → Gauge Protection → Hydraulics → Drilling Parameters → Field Performance

This is particularly important in mining applications, where formation conditions can change significantly within the same drilling pattern.

The objective is not simply to choose a bit with the "right" IADC number.

The objective is to find the bit design that provides the appropriate balance of:

ROP + Bit Life + Reliability + Total Drilling Cost

Tricone Bit University — Key Takeaways

If you remember only five things from this article:

1. The IADC code has three digits.

2. The first digit identifies the general cutting-structure / formation series.

3. The second digit provides a further formation classification.

4. The third digit identifies the bearing and seal configuration.

5. IADC classification is a starting point—not a complete bit specification.

The best bit selection combines the IADC classification with formation characteristics, drilling parameters, bit design, and actual field performance.

What's Next?

In the next edition of Tricone Bit University, we will go one step further:

IADC 517 vs. 537 vs. 637 vs. 725 vs. 745 — How Do You Choose the Right Tricone Bit for Your Formation?

Because knowing the IADC code is only the first step.

Knowing why one bit works better than another is where engineering begins.