Hole Inspection 240

This class explains different hole characteristics and describes how specific gages are used for different hole inspection applications. Includes an Interactive Lab.


Class Name:
Hole Inspection 240
This class explains different hole characteristics and describes how specific gages are used for different hole inspection applications. Includes an Interactive Lab.
Number of Lessons:
Additional Language:

Class Outline

  • Objectives
  • Hole Inspection
  • Hole Measurement
  • Out-of-Round Conditions
  • Contact Versus Non-Contact Instruments
  • Points of Contact
  • Variable Instrument Reading and Reporting Methods
  • Pin Gages and Plug Gages
  • Telescoping Gages
  • Split-Ball Gages
  • Calipers
  • Inside Micrometers
  • Bore Gages
  • Coordinate Measuring Machines
  • Optical Comparators
  • Borescopes
  • Laser Systems
  • Air Gages
  • Instrument Choice
  • Summary


  • Explain the purpose of hole inspection.
  • Distinguish between gaging and variable instruments.
  • Identify common out-of-round hole conditions.
  • Distinguish between contact and non-contact instruments.
  • Compare the number of points of contact an instrument provides with the type of instrument.
  • Distinguish between different types of variable instruments.
  • Describe the characteristics of pin and plug gages.
  • Describe the characteristics of telescoping gages.
  • Describe the characteristics of split-ball gages.
  • Describe the characteristics of calipers.
  • Describe the characteristics of inside micrometers.
  • Describe the characteristics of bore gages.
  • Describe the characteristics of coordinate measuring machines.
  • Describe the characteristics of optical comparators.
  • Describe the characteristics of borescopes.
  • Describe the characteristics of laser systems.
  • Describe the characteristics of air gages.
  • Describe the factors that influence instrument choice.

Job Roles


  • CNC Lathe Operations
  • CNC Milling Operations
  • Measurement, Materials, & Safety I
  • MSSC Quality Practices and Measurement


Vocabulary Term Definition
accumulated error The collected inaccuracy in measurement that can occur when multiple elements are combined.
accuracy The difference between a measurement reading and the true value of that measurement.
air gage A variable, non-contact pneumatic instrument that uses pressurized air to inspect the ID of holes.
air regulator The part of a pneumatic inspection system by which pressurized air is controlled.
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.
bore gage A hole inspection gage that makes three points of contact within the hole. Bore gages are handheld, mechanical or electronic contact instruments with variable measuring systems.
borescope A non-contact optical inspection device consisting of a rigid or flexible tube with an eyepiece at one end and a magnifying lens at the other. Borescopes provide a view of hole interiors that are otherwise difficult or impossible to see.
caliper A handheld, variable contact instrument that functions as a precision slide ruler. The indicators on the top of the instrument expand to measure internal diameters.
capable A gage's predictable range of ability, even when under the influence of natural variation due to common causes.
comparison device A measuring instrument that adjusts to assume the size of a feature.
concavity A curved surface condition like the inside of a ball.
contact instrument A measuring device that actually touches the part in order to obtain its measured value.
contact probe The main measuring member on a coordinate measuring machine that communicates its position on a workpiece to the CMMs control panel or computer. A probe often has a sphere of ruby at its tip.
continuous scanning An inspection method used by a coordinate measuring machine in which the probe slides along the surface of the workpiece to collect seamless data in the form of a series of numerous points.
coordinate measuring machine A sophisticated electronic measuring instrument with a flat polished table that inspects parts in three-dimensional space using either a contact or a non-contact probe. All CMMs are variable devices.
dial indicator A measuring instrument with a contact point attached to a spindle and gears that move a pointer on the dial. Dial indicators have graduations that allow you to read different measurement values.
digital readout An indicator on a measuring device that presents data through a numerical display.
electronic instruments Inspection devices that use electrical impulses to report either position changes or contact between the inspection device and the part.
extension A piece that is added to the head of an inside micrometer to expand it to the width of the hole.
eyepiece The part of a borescope through which the inspector views the interior of the workpiece.
flowmeter tube A cylindrical indicating device on a pneumatic measuring instrument that looks similar to a thermometer.
gaging instrument An inspection device of a standard size that determines fit but does not determine actual measurement value.
go/no-go gage An instrument that determines whether a part feature simply passes or fails inspection. No effort is made to determine the exact degree of error.
indicator A device, often numerical, that displays a measurement. An indicator may be a dial with a needle or a digital readout.
inner diameter ID. The interior surface of a hole in a workpiece.
inside micrometer A mechanical or electronic, variable, handheld contact instrument, usually cylindrically shaped, used to measure the inside diameter of larger holes.
laser system A non-contact, variable, optical inspection method that uses light to examine the inside diameter of holes. Laser systems send out a single light wave on a straight line that is detected by sensors and converted into an electrical signal.
light wave A form of visible energy used by lasers.
linear scale A series of parallel lines that represent a measurement standard. A ruler contains a linear scale.
linearity The amount of error change throughout an instrument's measurement range. Linearity is also the amount of deviation from an instrument's ideal straight-line performance.
lobing 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.
master gage A measuring device of a standard size that is used to calibrate other measuring instruments.
mechanical device A measuring instrument that must be physically manipulated by the inspector. Mechanical devices may be go-no go or variable.
micrometer head The main component of an inside micrometer that includes the scale and indicating device. Extensions are added to the micrometer head.
non-contact instrument A measuring device that is able to obtain the measured value of the part without making physical contact. An air gage is an example of a non-contact instrument.
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. Optical comparators are non-contact, variable, optical inspection devices.
optical instruments Inspection devices that use light and lenses to inspect parts. The part may be viewed directly through the lense or displayed on a screen.
outside micrometer A handheld device consisting of an anvil, a shaft, and an indicator that is used to measure outside diameters.
ovality A condition in which a hole that should be round has two opposing lobes, resulting in an egg shape.
pin gage A cylindrically shaped length of metal of a specific diameter used as a gaging inspection device. A pin gage is a handheld mechanical contact instrument.
plug gage A hardened, cylindrical gage used as a handheld mechanical contact instrument to inspect the size of a hole. Plug gages are available in standard diameters and are often two-sided, with a "go" side and a "no go" side.
pneumatic instrument A measuring device that uses a pressurized gas, such as air, to function.
precision The degree to which an instrument will repeat the same measurement over a period of time.
probe cable The portion of a laser system that transmits information and power to and from the tip of the device and the computer.
ring gage A circular measuring device of a standard size that is used to calibrate other instruments or inspect cylindrical parts.
rotary laser An inspection device that projects a light wave on the surface of the part's internal diameter as it turns.
scale A standard of measurement that is often displayed as a series of lines.
setting gage A measuring device of a standard size that is used to check or prepare a working gage for use. Bore gages often come with matching setting ring gages.
split-ball gage A cylindrical device with an expanding, flat-ended ball on one end and a locking device on the other. A split-ball gage is a handheld, mechanical contact instrument that is used for comparison measurement. It is also called a small-hole gage.
taper A gradual narrowing of an inside or outside surface.
telescoping gage A T-shaped measuring device that has two spring-loaded measuring arms and a lock in the base. A telescoping gage is a handheld, mechanical contact instrument used for comparison measurement.
thimble A ring or cylinder that fits around the spindle of a micrometer. To advance the spindle, you turn the thimble.
tolerance The acceptable variation from a specified dimension.
tolerance range The expected range of measurements produced by a given operation. It is also known as a tolerance zone.
variable instrument An inspection device calibrated in standard measurement units. Variable inspection reveals the degree of variation from a given standard.
video borescope A borescope that contains a video camera rather than an eyepiece.
working gage A measuring device of a standard size that is used to inspect parts.