Advanced Hole Inspection 341

Advanced Hole Inspection provides an overview of hole inspection using noncontact instruments. Holes that require a specific type of fit, either clearance, interference, or transition, also require a higher degree of accuracy. Noncontact hole inspection devices provide this, as well as an ability to measure fragile parts and high volumes of parts. These more sophisticated variable hole inspection devices include coordinate measuring machines, measuring microscopes, optical comparators, borescopes, laser systems, and air gages.

Job specifications, part dimensions, and feature size all determine which hole inspection device to use on holes requiring a certain fit. Choosing a tool without a high degree of accuracy could result in an out-of-tolerance hole passing inspection. After taking this class, users will be able to describe advanced methods for inspecting hole dimensions and geometric features in a lab setting.

  • Difficulty Advanced

  • Format Online

  • Number of Lessons 16

  • Language English


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Course Outline
  • Advanced Hole Inspection
  • Tolerances
  • Clearance and Interference Fit
  • Transition Fit
  • Noncontact Instruments
  • Inspection Facts
  • Borescopes
  • Air Gages
  • Inspecting with an Air Gage
  • Laser Systems
  • Hole Inspection Instruments
  • The Optical Comparator
  • Measuring Microscopes
  • The Coordinate Measuring Machine
  • CMM Hole Inspection
  • Advanced Hole Inspection Review
  • Explain the purpose of advanced hole inspection.
  • Identify methods of describing tolerance.
  • Explain the allowance for clearance and inference fits.
  • Explain the allowance for a transition fit.
  • Describe the characteristics of noncontact instruments.
  • Explain how to inspect holes using a borescope.
  • Explain how to inspect holes using an air gage.
  • Explain how to inspect holes using an air gage.
  • Explain how to inspect holes using a laser system.
  • Explain how to inspect holes using an optical comparator.
  • Explain how to inspect holes using a measuring microscope.
  • Explain how to inspect holes using a coordinate measuring machine.
  • Explain how to inspect holes using a coordinate measuring machine.
vocabulary term

air gage

A variable, noncontact instrument that uses pressurized air to pneumatically inspect a hole's inside diameter. Air gages are best for measuring features with tight tolerances.


The difference between the smallest permissible hole and the largest permissible shaft. An allowance creates a certain kind of fit between mating parts.

axial movement

Movement that occurs along or parallel to the axis of a part. A clearance fit allows for axial and/or radial movement.

backflow pressure

Movement of pressurized air in the direction opposite to which it was pushed out of the device. In an air gage, backflow pressure is caused by resistance from the sides of the hole.

bilateral tolerances

A tolerance method using an equal plus and minus deviation from the specified dimension. Bilateral tolerances are preferred if deviation in either direction risks exceeding the absolute limits and can be equal or unequal.


For use with both eyes simultaneously. A binocular eyepiece consists of two eyepieces fitted together side by side through which the user views the magnified object being inspected.

bore gage

A handheld mechanical or electronic contact variable measuring instrument that provides very accurate readings of hole sizes. A bore gage makes three points of contact within the hole.


A variable, noncontact inspection instrument that uses light and magnification to optically inspect a hole's ID without taking dimensional measurements. A borescope inspects deep holes and cavities visually for flaws using a tube fitted with a lens at one end and an eyepiece through which an inspector can view the part.

clearance fit

A fit that allows intentional space to exist between a hole and the shaft inserted into it. For a clearance fit, the shaft diameter is designed to be slightly smaller than the hole.

contact probes

A type of probe that directly contacts the surface of the part it is measuring. Contact probes are the most common type of CMM probes.

continuous analog scanning

CAS. A method of gathering coordinates that requires the stylus to stay in constant contact with the part's surface. CAS is especially useful for performing reverse engineering.

coordinate measuring machine

CMM. A sophisticated measuring instrument with a flat polished table and a suspended probe that measures parts in three-dimensional space. CMMs operate using either contact or noncontact methods.


The part of an instrument through which the inspector views the interior of the part. A borescope has either an eyepiece or a video screen through which an inspector examines the inside diameter of a hole.

fiber-optic cables

A group of thin, flexible glass or plastic optical fibers that are bundled together in a single cable and used to transmit light. Borescopes often use fiber-optic cables to connect the eyepiece to the probe.


A device that displays a measurement. An indicator may be a dial with a needle or a digital readout.

inside diameter

ID. The interior surface of a cylindrical workpiece or round hole. A borescope visually inspects a hole's inside diameter.

interference fit

A tight fit designed so that the smallest permissible shaft is larger than the largest permissible hole. Force is required to assemble parts with an interference fit.

laser probe

A measuring device that uses a narrow beam of light to take measurements. On a CMM, the laser projects onto the part's surface, and a lens on the probe then reads the beam's position.

laser system

A variable, noncontact inspection instrument that optically measures the distance between a light source and a hole's inside diameter. The laser system sends out a single light wave in a straight beam that is detected by sensors and converted into an electrical signal.

light wave

The pulsation in space that transmits light energy. Laser light waves are a form of visible energy which is detected by sensors.

limit dimensions

A tolerancing method using an absolute maximum and minimum allowable dimension. Limit dimensioning specifies a range of acceptable measurements instead of a target dimension.


A condition in which the manufacturing process creates a rounded projection out from what would otherwise be a circular hole. A hole may have more than one lobe.

measuring microscope

A variable, noncontact inspection instrument that uses light and magnification to optically measure part features, such as holes. Also called a toolmaker's microscope, the measuring microscope is useful for inspecting smaller parts and features.


For the use of only one eye. A monocular eyepiece consists of a single eyepiece through which the user views the magnified object being inspected.

noncontact probes

A type of probe that measures a part without directly contacting the surface of the part. A laser probe is one type of noncontact probe.

optical comparator

A sophisticated measuring instrument that projects an image of a part onto a screen to compare the shape, size, and location of its features to the original. Also called optical projectors, they can measure both surface and profile features of either the length and width of a part but not the depth.


An irregularly shaped hole that is not totally round. Many out-of-round conditions are caused by lobing.

pneumatic instrument

A device that uses a pressurized gas, such as air, to function. An air gage is an example of a pneumatic inspection tool.


A device on an inspection instrument that gathers measurement data from a part. On a borescope, the probe is the lens end that is inserted into the hole. On a CMM, the probe uses either contact or noncontact methods.

radial movement

Movement that occurs perpendicular to the axis of a part. A clearance fit allows for axial and/or radial movement.


A device that monitors the pressure level of the air in a pneumatic instrument. A regulator is one of the components in an air gage.


A grid of lines displayed in the eyepiece of an optical instrument. A reticle is used to measure part features on a measuring microscope.

rotary laser

A laser system that consists of a small revolving device attached to a probe which projects a light wave on the surface of the part being inspected. A computer then measures the distance between the center of the light source and the inside diameter surface.


The programs and instructions that control the computer hardware functions and operations. Operators use software on a computer to calculate measurements on a CMM.


A precision tip. On a CMM, the stylus is the spherical portion of the contact probe that is mounted on the shaft and makes contact with the part.


An unwanted but acceptable variation or deviation from a desired dimension of a part. A part within tolerances will meet specifications and pass inspection.

tolerance limits

A boundary of allowable variation from a specified dimension. Each machining operation has a different expected range of tolerance limits.

touch trigger probe

A type of contact probe that detects a feature on a part and generates an electronic signal to record its dimension. Touch trigger probes are the most accurate and commonly used probes on the CMM.

transition fit

A fit with an allowance that permits both a clearance and an interference fit. For a transition fit, a clearance fit occurs with the smallest shaft diameter and the largest hole diameter, but an interference fit occurs with the largest shaft diameter and the smallest hole diameter.

unilateral tolerances

A tolerancing method using a deviation in only one direction, either plus or minus, from the specified dimension. Unilateral tolerances are used if variation in only one direction risks exceeding the absoulte limits.

variable inspection

A type of inspection that reveals the degree of variation from a given standard. Variable inspection gives the actual measurement of a part feature that can be compared with its specifications.

video probe

A measuring device, also known as a vision probe, that takes a digital image of the part. The image is then broken up into tiny dots, which are measured and counted by the software.