Common Gauges and Measurement Instruments

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Quality control in manufacturing and engineering is a critical aspect that ensures products meet specific requirements and standards. One of the key competencies for quality professionals, such as those preparing for the American Society for Quality (ASQ) Certified Quality Inspector (CQI) exam, is the understanding of various measurement tools and gauges. These instruments are categorized based on the type of measurements they perform: variable, attribute, and transfer. Here's an overview of these tools for ASQ CQI candidates.

1. Variable Gauges

Variable gauges are instruments that measure and provide quantitative data on the dimensions of a component, allowing for a range of measurements.


Micrometers are precision instruments used to measure small distances with high accuracy. They typically consist of a calibrated screw and can measure thickness, lengths, and diameters. They come in different types, such as outside, inside, and depth micrometers, each suited for specific dimensions.


Calipers are versatile tools used to measure the distance between two opposite sides of an object. They come in several forms, including vernier, dial, and digital calipers. Vernier calipers use a sliding scale for measurement, while dial calipers show the reading on a dial. Digital calipers provide an electronic measurement display.

Dial Indicators

Dial indicators, also known as dial gauges or probe indicators, are instruments that measure small linear distances. They have a plunger that moves in and out to gauge the position of a surface relative to a reference position. These are commonly used for machine setup alignments and to check runout or roundness of parts.

Coordinate Measuring Machines (CMMs)

CMMs are advanced devices used for precise measurement of the physical geometrical characteristics of an object. They can be manually controlled or computer-aided and work by touching the part with a probe at different points to collect data points from the surface.

Linear Scales

Linear scales such as steel rules are basic measuring instruments with calibrated lines to measure lengths. They are simple yet essential tools in any quality inspector’s toolkit.

Gauge Blocks

Also known as Johansson gauges or slip gauges, these are systems of blocks with precisely machined lengths. They are used as references for calibrating measuring equipment and as precision spacers in setups.


Borescopes are optical devices used to inspect areas that are otherwise inaccessible. They are often used in non-destructive testing to visually inspect the interior of machinery or complex parts.

Thermometers and Temperature Probes

These instruments measure temperature. They range from simple analog thermometers to sophisticated digital devices with probes that provide real-time temperature readings of substances or environments.

2. Attribute Gauges

Attribute gauges are used to assess whether a part or feature is within specified tolerances or fits into a certain category.

Thread Plugs

Thread plug gauges are used to check the acceptance of internal thread, also known as female threads. They follow the principle of Go/No-Go where the Go side should thread in, and the No-Go side should not.

Progressive Rings

Progressive ring gauges are similar to thread plugs but are designed for external threads, also known as male threads. They also use Go/No-Go assessment.

Flush Pins

Flush pin gauges measure the depth of holes or slots, ensuring that pins or other components fit flush against a part's surface.

Pin Gauges

Pin gauges, also known as gauge pins, are precision measuring tools used to measure hole sizes and distances between holes. They come in various diameters and are used to check the tolerance of drilled holes.

Radius Gauges

Radius gauges measure the curvature of an object. They come in sets with various sizes and are matched against the workpiece to determine its radius.

3. Transfer Gauges

Transfer gauges are used to transfer the measurement of a dimension from the workpiece to a more readable measuring device.

Small-Hole Gauges

Small-hole gauges are used to measure the diameter of small holes. After being inserted into a hole, the gauge's end expands to fit the hole’s walls, and the measurement is then transferred to a more readable instrument, like a micrometer.

Telescoping Gauges

Telescoping gauges function similarly to small-hole gauges but are suited for larger diameters. They consist of a handle and two telescopic rods that are locked in place within a hole and then measured externally.

Spring Calipers

Spring calipers measure the distance between two surfaces or the thickness of an object. They come in three main types: inside, outside, and divider. The measurement taken is transferred to a ruler or other scale for reading.

These instruments are fundamental for quality inspectors and understanding their application is crucial for ASQ CQI exam candidates. 

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