This document discusses various measurement devices and systems used in automotive repair. It describes the United States Customary and metric measurement systems, with the inch and meter as their base units respectively. It provides details on common measurement tools like rulers, feeler gauges, micrometers, dial indicators, calipers, and gauges for measuring pressure and vacuum. Proper tool selection and technique are emphasized for obtaining accurate measurements.

1. Measurements and Precision
Measuring Devices

2. Introduction
 Methods of collecting data depend on what is being
measured
 Check for excessive wear or damage when servicing
components
 Some shops send components out for these
measurements and tests
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3. Measuring Systems
 Most common measurement in the U.S. is the United
States Customary (USC)
 Based on the inch ( 1” )
 Can be measured in decimals (1.000”) or fractions (1/16”)
 Engine measurements are expressed in thousandths of an
inch (0.001”)
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4. Measuring Systems
 Metric system based on the meter
 Most common units in the automotive industry are the
centimeter (1cm) and millimeter (1mm)
 Millimeters are used to express close tolerances of
engine measurements
 Metric system is based on divisions of ten
 10mm=1cm
 10cm=1dm
 10dm=1 meter
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5. Measurement Conversion
 Sometimes needed-measurement specifications are
not stated in the necessary format
 Ensure correct conversion factor is being used at all
times
 Sometimes conversion charts are readily available
 Key Notes page 44 has conversion chart
 To convert inches to mm, multiply inches by 25.4
 To convert mm to inches, divide mm by 25.4
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6. Rulers and Feeler Gauges
 Rulers
 Simple tools to measure straight-line distances
where tolerances are not a major factor
 May be USC or metric
 Can be made of metal, plastic, or wood
 Typical rulers are 6 inches or 12 inches
 Drafting rulers can have several different scales
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7. Typical Machinist Ruler
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8. Rulers and Feeler Gauges
 Feeler Gauges
 Precision-machined piece of metal that is flat or
round
 May be USC or metric
 Used for measuring “gaps” or the space between two
objects
 Proper usage requires practice
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9. 12

10. Micrometers and Associated
Gauges
 Micrometers precisely measure different shapes of
a component
 Outside micrometers
 Resembles a clamp to measure linear distances
 Proper use requires practice and studying the
markings of the instrument
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12. Micrometers and Associated
Gauges
 Micrometer Limitations
 In order to measure accurately, the micrometer must
be accurate itself
 User experience and “feel” can affect accuracy
 Extreme temperatures can also affect accuracy
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13. Micrometers and Associated
Gauges
 Micrometer Calibration
 Performed using a standard gauge and an adjusting
tool
 Use proper length gauge for micrometer being
calibrated
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14. Micrometers and Associated
Gauges
 Reading a USC Outside Micrometer
 Place anvil against work
 Rotate thimble to bring spindle into contact with
opposite side of work
 Use ratchet knob to ensure sufficient contact is made
 Remove micrometer and read dial
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15. Micrometers and Associated
Gauges
 Reading a Metric Outside Micrometer
 Similar to USC micrometer except for size of scales
 Measurements vary from USC
 Follow steps in text
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16. Micrometers and Associated
Gauges
 Telescopic Gauges
 Used with outside micrometers to measure inside
diameters
 Various lengths and T-shaped
 Extensions are spring-loaded
 Accuracy subject to user experience
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17. Micrometers and Associated
Gauges
 Telescopic Gauges
 Leg has a rotatable handle to lock extensions in place
 Once gauge is removed, measure with outside
micrometer
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18. Micrometers and Associated
Gauges
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Telescopic Gauges

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20. Micrometers and Associated
Gauges
 Inside Micrometers
 To measure inside of large holes
 May be USC or metric
 Spindles of different lengths can be installed to
match hole size
 Requires skill and practice for accurate
measurements
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21. Small Hole Gauges
 To measure small holes
 Gauge is straight with a screw handle on one end and a
split ball on other
 Handle is turned to expand ball
 Removed and measured with a micrometer
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22. Dial Indicators and Calipers
 Dial Indicators
 Easy way to check how far components can move
 Scale can be USC or metric
 Face can be balanced or continuous
 Used to check run-out or end-play
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23. Dial Indicators and Calipers
 Dial Calipers
 For inside, outside, and depth measurements
 Manual scales or digital
 USC can measure in 0.001 inch increments
 Metric can measure in 0.02 millimeter increments
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24. Pressure and Vacuum
Measurements
 Pressure Gauges
 Measure amount of pressure applied to a closed,
sealed system such as oil pressure system
 Fitted into pressure line with appropriate fittings
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25. Pressure and Vacuum
Measurements
 Vacuum Gauges
 Mechanical gauge measures difference between
atmospheric pressure and current state of system
 Most common use is to measure mechanical
condition of engine
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26. Summary
 Most common measurement system in United States
is the United States Customary or the English system
 Base USC measurement is the inch
 Base metric measurement is the meter
 Use proper measuring tool for the job
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