Last revised: January 9, 2025

Reviewed by: Scott Orlosky, consulting engineer

Bore gages and ID gages are designed for dimensional measurement or assessment of the internal diameter of components.  Bore gages and ID gages are available that employ variable or fixed mechanical, electronic or pneumatic technologies. Specialized bore gaging tools have the capability to measure the degree of roundness (lobes), taper or internal steps, grooves or serrations.  Some devices are set to test for a standard bore gage, displaying a deviation from the norm, while others are designed to simply measure the component in question.

Types of Bore Gages and ID Gages

Mechanical Gages

Mechanical bore gages use comparison or the physical movement and displacement of a gaging element (e.g., spindle, slide, stem) to determine the dimensions of a part or feature.  Bore micrometers, calipers, indicators, plug gages, ring gages or snap gages are examples of mechanical gages.

Electronic Bore Gages

Electronic gages use LVDT, capacitance, inductive or other electronic probes to sense the distance or displacement of a contact or stylus.  Mechanical gages such as micrometers, plug gages, and snap gages may employ an integral electronic probe in addition to the mechanical gaging elements.

Air Bore Gages

Pneumatic gages or gaging systems use the changes in flow or pressure in air nozzles or inlets internally located in air plugs, probes, rings or snaps or other pneumatic gages.  Pneumatic comparators, digital readouts, analog amplifiers, columns or flowmeter / rotameter tubes are used to display air gaging dimensional data.

Other Types of Bore Gages and ID Gages

Specific types of bore gages and ID gages include internal calipers, slot gages, indicating bore gages, dial bore gages, and 3-point bore gages.  

Calipers

Calipers use a precise slide movement for inside, outside, depth or step measurements. While calipers do not typically provide the precision of micrometers, they provide a versatile and broad range of measurement capabilities: inside (ID), outside (OD), depth, step, thickness and length. Shop tool, spring-type or firm joint calipers consist of two legs with a scissor action and are usually used for comparative gaging or measurement transfer; although some spring-type calipers have dial indicators.  

Slot Gages

Slot gages are expanding collet type gages used for comparative measurement of small holes.  The gage is expanded in the hole and then removed and measured with a micrometer or other external (OD) gage. Alternately, the hole or slot gage can be set and used to check if a hole is above or below a specific size or tolerance. 

Indicating Bore Gages

Indicating bore gages are gaging devices for comparative measurements where the linear movement of a spindle or plunger is amplified and displayed on a dial, column or digital display.  Typically, indicators have a lower discrimination (0.001" to 0.0001") and greater range (+/- 1.000" to +/- 0.050" total) compared to comparators.  The level or precision is sufficient for measurement of precision ground parts and for the calibration of other gages.    

Three Point Bore Gages

Three-point bore gages have three contact points mounted on arms that expand out from a central point. Three-point bore gages can detect lobe or out-of-roundness conditions, which is an advantage over two-point ID gages. These gages can have either a dial bore indicator or a digital display.    

Related Standards

• NPFC - A-A-58070  — Gage, Indicator Bore
• TM 9-4933-200-35 — Pullover Gages Borescopes M1/M2 Pressure Gage M3
• ASME B89.1.6 — Measurement Of Plain Internal Diameters For Use As Master Rings Or Ring Gages

Bore Gages and ID Gages FAQs

What are the key differences between bore gages and ID gages in terms of measurement accuracy?

Types of Measurements

Bore gages are specifically designed for measuring the diameter of bores, which is a critical dimension in many engineering applications. They are often used for precision measurements where high accuracy is required, such as in the manufacturing of engine and transmission components.

ID (Internal Diameter) gages, on the other hand, are used for measuring the internal dimensions of various components. They can be part of systems that measure both internal and external dimensions, offering versatility in measurement tasks.

Measurement Techniques

Bore gages can include electronic, pneumatic, and mechanical types. Electronic bore gages use probes to sense displacement, while pneumatic gages use changes in air flow or pressure to measure dimensions.

ID gages may also use similar technologies but are often part of more comprehensive systems that can switch between measuring internal and external dimensions, which might affect their precision in specific applications.

Precision and Accuracy

Indicating bore gages are noted for their precision in comparative measurements, with a discrimination range from 0.001" to 0.0001", which is suitable for precision ground parts.

The accuracy of ID gages can vary depending on whether they are dedicated to internal measurements or part of a combination unit that measures both internal and external dimensions. Combination units offer advantages in versatility but may not match the precision of dedicated bore gages in specific applications.

What are the advantages of using combination units for ID and OD measurements?

Cost Efficiency

Combination units eliminate the need for duplicated sensors, which can lead to significant cost savings.

Space Optimization

These units require less bench space compared to having separate machines for ID and OD measurements, making them ideal for environments where space is a constraint.

Ease of Use

Technicians only need to become proficient with one machine instead of multiple devices, simplifying training and operation.

Versatility and Flexibility

Combination units allow for quick switching between OD and ID measurements, enhancing the versatility and flexibility of measurement tasks.

These advantages make combination units a practical choice in many engineering and manufacturing settings where both internal and external measurements are frequently required.

What are the advantages of electronic bore gages over pneumatic ones?

Precision and Accuracy

Electronic bore gages utilize electronic probes such as Linear Variable Differential Transformers (LVDT), capacitance, or inductive sensors to measure displacement with high precision. This allows for very accurate measurements, which are crucial in applications requiring tight tolerances.

Data Integration and Output

Electronic bore gages typically provide digital readouts, which make it easier to interpret and record measurements. They can also be integrated with data acquisition systems, enhancing the ability to analyze and store measurement data efficiently.

Versatility

Electronic gages can be used in a variety of applications beyond just measuring bores, such as measuring outside diameters, hole depth, and other dimensional characteristics. This versatility can be advantageous in complex engineering environments.

What are the limitations of electronic bore gages compared to pneumatic ones?

Sensitivity to Environmental Conditions

Electronic bore gages may be more sensitive to environmental conditions such as temperature and humidity, which can affect electronic components and lead to measurement errors. Pneumatic gages, on the other hand, rely on air pressure and flow, which might be less susceptible to such environmental variations.

Complexity and Maintenance

Electronic systems can be more complex and may require more maintenance due to the presence of electronic components and sensors. This complexity can lead to higher maintenance costs and the need for specialized training for operators.

Initial Cost

The initial cost of electronic bore gages can be higher due to the advanced technology and sensors used. Pneumatic gages might offer a more cost-effective solution for certain applications, especially where high precision is not as critical.

Which applications might pneumatic bore gages be preferred over electronic ones?

Environmental Conditions

Pneumatic bore gages are less sensitive to environmental conditions such as temperature and humidity. This makes them suitable for use in environments where electronic components might be affected by such conditions, potentially leading to measurement errors in electronic gages.

Cost Considerations

Pneumatic gages might offer a more cost-effective solution for applications where extremely high precision is not critical. The initial cost of pneumatic gages can be lower compared to electronic gages, which use advanced technology and sensors.

Simplicity and Maintenance

Pneumatic systems are generally simpler and may require less maintenance compared to electronic systems. This simplicity can be advantageous in settings where ease of maintenance and operation is a priority.

What is the role of data integration in electronic bore gages?

Improved Data Management

Data integration in electronic bore gages allows for seamless connection to data acquisition systems. This capability enables the efficient collection, storage, and analysis of measurement data, which is crucial for quality control processes.

Enhanced Quality Control

By integrating data from electronic bore gages into a centralized system, organizations can improve the level of quality control. This integration supports the tracking of measurement trends and the identification of potential issues in manufacturing processes, leading to more informed decision-making.

Automation and Efficiency

Data integration facilitates automation in measurement processes. Electronic bore gages can automatically transmit data to software systems, reducing the need for manual data entry and minimizing the risk of human error. This leads to increased efficiency and accuracy in measurement tasks.

Real-Time Monitoring

With integrated data systems, real-time monitoring of measurements becomes possible. This allows for immediate feedback and adjustments during the manufacturing process, ensuring that components meet specified tolerances and reducing the likelihood of defects.

Bore Gages and ID Gages Media Gallery

References

Marposs— Hand Held Gauges For Quality Control Of Engine And Transmission Cases