How to Use a Bore Gauge

How to Use a Bore Gauge

If you’ve ever needed to measure the depth or diameter of a hole, you’ve probably heard about bore gauges. These tools make accurately measuring the size of a hole simple and easy.

At first glance, bore gauges can look complicated with their buttons, symbols, and dials. But once you understand how they work, they’re a breeze to use.

What is the Purpose of a Bore Gauge?

A bore gauge is a specialised instrument designed for measuring the internal diameter (ID) of a pipe or hole. They’re commonly made of steel and are highly precise, with a margin of error within micrometres.

You might use a bore gauge to measure:

  • Metal, fibreglass, and plastic pipes
  • Rubber tubing
  • Holes in metal sheets
  • Holes in wood, plastic, or rubber

Bore gauges are a common sight in industries such as manufacturing, fabrication, construction, automotive, and engineering.

How to Use a Bore Gauge to Measure Internal Diameter

For the purpose of this guide, we’ll talk about dial bore gauges specifically. Before starting, make sure you have the right tools on hand. You’ll need:

  • Dial bore gauge
  • Micrometre
  • Pencil and paper
  • Table vice

Now, let’s dive into the steps you’ll need to follow to take your measurement.

  1. Make sure the head on your dial bore gauge matches the size of the hole you’re measuring. A typical dial bore gauge kit will offer sizes ranging from 8mm to 150mm.
  2. Now it’s time to ‘zero’ the gauge. Place the bore gauge into your micrometre. Make sure it’s locked to the diameter of the hole you’re measuring.
  3. Rotate the dial until its pointer aligns with the ‘0’ symbol on its face—you’ve now successfully ‘zeroed’ the gauge and are ready to begin your measurement.
  4. Insert the bore gauge into the hole to the desired depth while ensuring both anvils touch the wall. Rock the gauge back and forth (while keeping the anvils straight) until it is properly situated within the pipe or hole.
  5. Now the bore is set, check the dial face. Its pointer will start reversing, heading left or right of the ‘0’ marker. Note where the needle falls. If it stops to the left, the measurement is negative, meaning the bore exceeds its clearance specifications.
  6. Remove the gauge from the hole.

Now you have your reading; it’s time to calculate the final measurement.

Understanding the Bore Gauge Measurement

Take the target number you calibrated the indicator to and the recorded reading to calculate your final measurement. Depending on how the pointer travelled when you took your measurement, you’ll need to add or subtract the recorded reading from the target number.

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For example, let’s say you calibrated the gauge to five centimetres, the indicator moved to the right, and you took a reading of 0.018mm. The final measurement, then, would be 5.018 centimetres.

On the other hand, if the indicator moved 0.018mm to the left, the final measurement would be 4.982 centimetres.


Now you understand how bore gauges work and their common applications, you should have no trouble using the device to take precise, accurate diameter measurements.


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