What Is A Bore Gage?


As a calibration company, we often faced with the challenge of what do you call it.

Cylinder Test. Hole Test. Bore Mic. Holtest. Internal Micrometer. Hole Bore Gage. Telescoping gage.

What Is A Bore Gage?

A Bore Gage is used to measure the inside diameter of a hole or cylinder. This explains why it is referred to by so many different names. You are actually measuring the bore size.

A bore is simply a hole and a bore gage measures the internal diameter of the hole. This should not be confused with the other type of bore that drives you crazy at social events.

How does a bore gage work?

A bore gage has anvils that expand to touch the surface of a bore and measure the inside diameter.

They can be dial or digital.

what is a bore gage dial alliance calibration.jpg

      what is a bore gage digital alliance calibration.jpg

Some are mounted in a handle and look like a caulking gun or pistol.

what is a bore gage pistol alliance calibration.png

How do you set a bore gage?

A typical bore gage will have two anvils.

The best method is to wring gage blocks together and measure the internal diameter.

bore gage calibration alliance calibration 

What standards apply to Bore gage calibration? ASME B89 1.21  Bore Gages was consolidated into ASME B89 1.9 Gage Blocks standard. You will also see a reference to T.O. 33K6-4-992-1 which is an Air Force calibration reference.

So where is the setting ring?

A two anvil bore gage is calibrated with gage blocks. A multi anvil gage used for measuring internal diameters is an Internal Micrometer and commonly referred to as a Tri Mic. You would use a setting ring for calibration of these types of micrometers.

Internal Micrometer alliance calibration.jpeg            Hole micrometer alliance calibration.jpg


We leave all the names for an Internal Micrometer for another blog.

You may want to visit our Visual Index to see the types of gages and equipment we calibrate.

Phil Wiseman

Phil Wiseman

Phil Wiseman is Chief Marketing Officer at Alliance Calibration. He earned a B.S. in Chemical Physics from Centre College. Phil is an ASQ Certified Quality Auditor and ASQ Certified Manager of Quality/Organizational Excellence.

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