What Size RC PDC Bit Do I Need?

RC PDC Bit Size Chart, Selection Guide & Common Mistakes

Choosing the correct RC PDC bit size is one of the most critical decisions in reverse circulation drilling. The right size ensures stable drilling, accurate sample recovery, and maximum bit life—while the wrong choice can lead to poor sample quality, excessive wear, or even tool failure.

This guide explains RC PDC bit sizes, provides a clear size chart in inches and millimeters, and shows how to select the correct diameter for your drilling application.

What Is the Standard Size Range for RC PDC Bits?

Quick answer:
Most RC PDC bits are manufactured in sizes ranging from 3 1/2 inches to 5 inches, depending on the RC hammer, sample tube diameter, and formation conditions.

Unlike conventional RC bits, RC PDC bits must balance outer diameter stability with internal flow capacity, making size selection more technical than simply “matching the hole diameter.”

RC PDC Bit Size Chart (Inches & Millimeters)

Below is a typical RC PDC bit size reference used in mineral exploration, geotechnical drilling, and RC drilling programs.

Why RC PDC Bit Size Matters More Than You Think

1. Sample Quality and Recovery

RC drilling relies on efficient cuttings transport through the internal sample tube.
If the bit size is not properly matched:

• Cuttings may mix or degrade

• Sample recovery rate drops

• Geological data accuracy is compromised

A correctly sized RC PDC bit maintains stable hole diameter, producing cleaner and more representative samples.

2. Drilling Efficiency and Penetration Rate

Oversized or undersized bits can cause:

• Excessive torque

• Bit vibration

• Reduced rate of penetration (ROP)

PDC cutters perform best when contact pressure and cutter exposure are balanced, which is directly influenced by bit diameter.

3. Bit Life and Cost Control

Improper sizing accelerates:

• Gauge wear

• Cutter chipping

• Shoulder damage

Selecting the correct size helps extend cutter life and reduce replacement frequency, especially in abrasive formations.

How to Choose the Right RC PDC Bit Size

Step 1: Confirm RC Hammer & Inner Tube Size

Always start with your RC hammer specifications:

• Inner tube diameter

• Airflow capacity

• Maximum allowable bit OD

The RC PDC bit must allow smooth cuttings return without restriction.

Step 2: Evaluate Formation Conditions

In hard formations, diameter stability is more important than aggressive cutting, making PDC-based RC bits highly effective.

Step 3: Consider Sampling Accuracy Requirements

If your project demands high sample integrity (e.g., mineral exploration):

• Avoid oversized bits

• Prioritize controlled cutting and smooth airflow

• Use RC PDC bits with optimized internal flow channels

Common RC PDC Bit Size Selection Mistakes

X Choosing Based on Hole Size Alone

RC PDC bits are not conventional drag or tricone bits. Internal design matters as much as outer diameter.

X  Ignoring Internal Flow Area

A larger OD with poor internal clearance can cause sample blockage or loss.

X  Oversizing to “Drill Faster”

Bigger is not always better. Oversized bits increase torque and vibration, shortening bit life.

RC PDC Bit vs Conventional RC Bit: Size Stability Comparison

This is why RC PDC bits are increasingly preferred in modern RC drilling programs.

RC PDC Bit Size Options from GreatDrillbit

GreatDrillbit manufactures RC PDC bits in a wide range of standard and custom sizes, designed for:

• High-impact resistance

• Stable gauge protection

• Optimized airflow and sample return

Our RC PDC bits feature carefully arranged PDC cutters and reinforced shoulders, ensuring consistent diameter control even in abrasive or fractured formations.

Learn more about our RC PDC bit solutions:

Reverse Circulation PDC Bit For Geological Exploration Samples | GREAT Bit