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Feeler gauge| Types of Feeler gauge| Use of Feeler Gauge| Size of feeler gauge

What is feeler gauge?

A Feeler gauge is used to measure the clearance between two parallel flat faces for example piston and cylinder. As the name suggests, feeler gauge called as to measure neither tide nor freely.

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feeler gauge

Feeler gauges are used for measurement of clearances.

It is a tool that measures air or narrow gap widths between two surfaces in engines and machinery.

Size of Feeler gauge

Feeler gauge available in no. of the blade like 10,13,20 and 28. With a step of 0.05 and 0.10 mm.

The thickness of the blades are in fractions of mm and inches, usually ranging from 0.03 mm to 1mm.

leaf of feeler gauge

Parts of Feeler gauge

The feeler gauge has two major parts, a  body or block which acts like a protective case or shealth and a large number of blades of different thickness.

The body is the base that holds the blades together. Feeler gauges are made entirely of steel so that they are corrosion free and the blades do not rust easily.

In machinery and engine service, it is important to predict accurate measurement of gaps for smooth performance and to avoid any faulty operations.

It is extensively and mostly used for measuring the gap between an engine cylinder and piston.

When there is extra gap even after a blade is inserted then the blades of the feeler gauge can be used in various combinations as per the requirement, that is different blades having different thickness can be stacked together and used.

How to use Feeler gauge?

The working of feeler gauge is easy. The blades are kept on the vacant gap that needs to be measured, initially one blade of standard thickness is kept, then if there are extra gaps other blades are adjusted and joined together and used.

Ensure that the blades can be easily pushed to and fro and are not tight nor free to move.

In order to have a problem-free measurement, the blades should be free of dirt and grease.

Feeler gauge look like same to Radius gauge.

To maintain the blades for longer lifetime apply motor oil after every use.

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Do you know How to Measure strain?

We all know about stress and stain and and its relation. But have you ever know about the measurement of Strain. please comment your valuable response.

The strain gauge is fundamental of many type of sensors like pressure sensors, load cells, torque sensors etc.

The most common form of strain gauge is the electrical resistance strain gauge.

The gauges are formed by either a length of wire arranged in an axial grid pattern or by etching a thin metal foil into the desired shape.

By Izantux – WikiCommons, CC0,

Most strain gauges are foil types.

Foil Strain gauge

By Pleriche – Own work, CC BY-SA 4.0,

Foil stain gauges are available in a wide choice of shapes and sizes to suit a variety of applications.

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They operate by simple principle i.e. As the foil is subjected to stress, the resistance of foil changes in defined way.

Normally, wire gauges are used for high temperature applications and foil gauges are used for routine applications.

Some important parameter about Foil gauges are

  • High stability
  • Good proportionality
  • Easy manufacturing
  • Low output voltage(requires amplification)

A strain gauge’s conductors are very thin if it made of round wire, about 1/1000 inch in diameter.

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What is Transducer? and it’s classification

We know that the generalized measuring system consists of three functional elements(transducer is first stage):

  1. primary detector-transducer stage,
  2. intermediate modifying stage, and
  3. the output or terminating stage.

 Each stage performs certain functions so that the value of the physical variable to be measured (measurand) is displayed as output

What is Transducer?

A transducer is a device that converts one form of energy into another form.

signal process of transducer
By Brews ohare – Own work;… Uses File:EAR.jpg and File:Sexy-Red-Lips Happy-Girl.jpg, CC BY-SA 3.0,

 The transducer, which may be electrical, mechanical, optical, magnetic, piezoelectric, etc., converts the sensed information into a more convenient form.

The detecting or sensing element of a measuring system first makes contact with the quantity to be measured, and the sensed information is immediately transduced into an analogous form.

Classification of Transducers

Analog and Digital Transducers

 In the case of analogue transducers, the input quantity is converted into an analogue output, which is a continuous function of time.

pressure transducer
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LVDT, strain gauge, thermocouple, and thermistor are some examples of analogue transducers.

 If a transducer converts the input quantity into an electrical signal that is in the form of pulses, as output, it is called a digital transducer.

These pulses are not continuous functions of time but are discrete in nature. Examples are shaft encoders, linear displacement transducers.

Terminating Devices

Meter Indicators

Meter indicators can be categorized as follows:

  1. Simple D’Arsonval type to measure current or voltage
  2. Volt–Ohm milliammeters or multimeters
  3. Vacuum tube voltmeters

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Simple D’Arsonval Type to Measure Current or Voltage

 It essentially consists of components like a permanent

magnet, coil, hairsprings, pointer, and scale. The coil assembly is mounted on a shaft, which in turn is hinged on a hair spring.

 To concentrate the magnetic fields, initially, the iron core is placed inside the coil.

 The curved pole pieces are then attached to the magnet to ascertain if the torque increases as the current increases.

This means that electromagnetic energy is used to move the meter.

Volt-Ohm Milliammetersor Multimeters 

The typical volt–ohm milliammeter employs switching provisions for connecting multipliers, shunt resistors, and rectifier circuits.

The current flowing through the resistor can easily be determined by switching over to the ohm-meter function, wherein the leads can be connected to the unknown resistance that causes the meter movement.

The advantage is that direct measurement is possible since the current flow indication is calibrated in terms of resistance

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Vacuum Tube Voltmeters

The vacuum tube voltmeter, popularly known as VTVM, is basically used to measure voltage.

To control the grid of the tube, proper multiplier resistors are employed through which the AC or DC input is given to the meter.

The input resistance of a VTVM is usually very high, when compared to that of a simple meter, due to high grid circuit resistance. This minimizes the loading of the signal source.

Cathode Ray Oscilloscope

 A CRO is a voltage-sensitive device that is used to view, measure, and analyse waveforms.

Its advantage is that a beam of electrons with low inertia strikes the fluorescent screen, generating an image that can rapidly change with varying voltage inputs to the system.

 The cathode ray tube (CRT) is the basic functional unit of CRO. The electron gun assembly comprises a heater, a cathode, a control grid, and accelerating anodes. When a cathode is heated, electrons are generated.

The accelerating anodes, which are positively charged, provide the necessary striking velocity to the emitted electron stream.

The electron beam, after gaining necessary acceleration, passes through horizontal and vertical deflection plates, which provide the basic movements in the X and Y directions.

XY Plotters

The XY plotters generate Cartesian graphs, which are obtained by two DC inputs, in X and in the Y-axis. It consists of two self-balancing potentiometers, one to control the position of the paper and others to control the position of the pen.

 In XY plotters, the output is generated by plotting one emf as a function of the other emf.

 Further, the emf, which is the output signal of transducers, may be a value of displacement, force, pressure, strain, or any other parameter.

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Metrology Terminologies

Measurement is a Natural part of everyday life. We express daily needs in size & weights, water and electricity are also metered.

A number of blood samples, active sub-stain in medicine also needs to be precise.

I think it is Impossible to describe anything without measuring it.

measurement tools
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Room temperature, body weight, sunshine,chest width and so on..

Almost every company are concerned with Quality management in the process of Introducing their work

First, we try to understand what is Metrology!

What is Metrology?

Metrology word derived from the Greek words Metro(means Measurement) and Logy(means Science).

Metrology includes all aspects with reference to measurements, whatever their level of accuracy.


Some technical terms are difficult to understand, so the following terminology is quite helpful for further studies


Accuracy is the closeness between a test result and accepted value.


Bias is the difference between the expected value and the accepted reference value.


Calibration is the set of operations that establish under specified conditions, the relationship between values of quantities indicated by a measuring instrument or values represented by a material measure and the corresponding values realized by standards.


Drift is slow to change of a metrological characteristic of measuring instrument.


The output result from a measuring device to be magnified many times to make it more readable, called Magnification.


Precision is the closeness of agreement between independent test results obtained under stipulated conditions.


The smallest change of the measured quantity which changes the indication of a measuring instrument is called Resolution.


Traceability means a measured result can be related to references.

Read more, about Units of Metrology

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Why Measure Depth by Depth Micrometer why not Vernier caliper?

We also measure depth through Vernier caliper, but Vernier caliper does not deliver as much as accuracy and precision, because extension rod of Vernier caliper has no standard, it used only for comparison purpose.

depth vernier

Depth micrometer used to measure the depth of an object with precision and accuracy with least count of 0.01 mm. The measuring span is 25 mm just like in micrometer, that can change by changing upsetting rod.

How to Measure with Micrometer?

Depth Micrometer

Measuring Concept of Depth Micrometer is same as External Micrometer. The main differences are direction and position. Reading scale is Vertical in-depth micrometer and Direction of reading is opposite (starting from the end scale).

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Some normal characteristics of Depth Micrometer describe follows


The accuracy of Depth Gauge is 0.01 mm which is fair enough for linear measurement and also accurate than vernier caliper. You can choose Digital Depth Micrometer, in order to simplify observation only. Both types of Depth Micrometer delivers the same accuracy.


Depth Micrometer follows national or international measurement standard, while vernier caliper is not(in order to check depth through extension rod only).


The cost of Depth Micrometer is low than digital type. Cost may be varied brands to brands, usually depend upon the quality of material used. Some most famous Brands which are known for their quality promise available in a market like Mitutoyo, baker etc.

The main use of depth micrometer is to check the depth of any objects. Basically used in industrial areas of manufacturing plants.

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Inside Micrometer & Least count

Inside Micrometer is used to measure the larger internal dimension. Inside Micrometer can measure internal Diameter of holes and registers.

inside micrometer
Mitutoyo’s Inside Micrometer

Types of Micrometer

There are various types of micrometers available in the industry each used for a specific purpose. One such micrometer is the “Inside Micrometer”.The inside micrometer is used to measure the inner diameter of objects that are bonded by walls,cylindrical bore or hollow pipe.There are two types of Inside Micrometer

  1. Analog type Inside Micrometer
  2. Digital type Inside Micrometer

The least count is 0.01 mm for analog type and 0.001 mm for digital type.

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It can be measured by mm or inches and gives precise readings. The inside micrometers are also available in different designs and sizes for various measurements.

digital inside micrometer

The general equipment comprises of a measuring head or a micrometer unit; extension rods; spacer or spacing collar and a handle.

The measuring head consists of a thimble, which has one way marking and holds readings up to 50 mm which is the thimble division(TD) reading.

The sleeve or barrel have the main or index scale and sub-scales, they have two waymarking. The main scale can measure up to 25 mm and the measured value is known as MSD(main scale division).

On the frontier end of the measuring head which is also known as the anvil is a hole through which the extension rods are inserted to the inside micrometer. On one side of the anvil is a locking screw that is used to adjust the extension rods and holds it firm. On the other side, there is a hole that is used to fit the handle.

The handle is used to insert the inside micrometer through objects having depth. The posterior end also contains a screw that is used to adjust the thimble.

Range of inside Micrometer

Good quality steel is used in measuring head and spindle, but for the faces-high graded tool steel is used. The least count of the inside micrometer is 0.01 mm. The extension rods can be of different sizes ranging from 50 mm- 200mm, depending on the requirement.

inside micrometer 50-150
MItutoyo’s Micrometer

The extension rods are classified as

  • 50-75mm;
  • 75-100mm;
  • 100-125mm;
  • 125-150mm;
  • 150-175mm;
  • 175-200mm

.Extension rods are used for extensive objects having large diameters, it is used along with the spacer. The spacer is used for smaller diameter in addition to the measuring head. The spacer is of 12 mm.

How to measure inner diameter with Inside Micrometer?

The design of inside micrometers can also have jaws where one end is fixed and the other is movable.The working of inside micrometer is very simple.It basically consists of three steps

  1. fixing the rod and spacer
  2. adjusting the screw and
  3. measuring.

Its working same as analog type micrometer you can check here: External Micrometer

Precise readings are necessary to prevent faulty readings and leakages that can cause errors.

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What is Radius Gauge?

During the early period, there were no units for measuring thickness, which leads to the invention of the gauge.

radius gauge kresteel

Gauges are derived from the French word”jauge” which means the result of the measurement. We are all aware that gauges are used to measure the thickness, size or capacity of something.

concave and convex shape

Likewise, radius gauges are instruments that are used to measure the radius of the object.

blades of radius gauge

The radius gauge is combined with another gauge known as fillet gauge which in mechanics means a rounding of the part design.

kristeel radius gauge

Radius gauge is a radius measurement tool that can be used to measure the inner radius whereas the outer radius is measured by the fillet gauge.

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The construction of the radius gauge consists of two gauges having a number of steel strips or blades screwed together in one single holder. The screw is known as the lock screw.

parts of radius gauge

The radius measurement is usually in metric form and measured in mm(millimeter). The material used is entirely made up of stainless steel, but a  layer or finish of satin chrome can be added since it keeps the radius gauge corrosion free and gives them more rust resistance.

The blades used are of the concave and convex shape. It may be swung out of the holder case when necessary readings need to be taken as per the requirement.

radius gauge

The markings are inscribed on the upper surface of every individual blade

Types of radius gauge

Three sets of radius gauge are manufactured.

  • Set 1 measure the radius available from 0.6-0.8mm.
  • Set 2 measures 1-7mm,
  • Set 3 measures 3-8.25mm.

The object or workpiece whose radius is to be measured is taken and the blades are inserted one by one to check which one fits in exactly by comparing it with the radius on the object.

Specifications of radius gauge

The radius gauge is light in weight and has an attractive design. The world keeps evolving and new and advanced technologies are taking over the old methods, hence a more optimistic and advanced gauge known as “digital radius gauge” is also available.

radius and fillet gauge

It is used for obtaining a high level of precision. It is a measuring tool that is user-friendly and the end user can operate it with great ease, fast since it is digital and portable.

Construction of radius gauge

T he construction of a digital radius gauge is entirely different than that of a simple radius gauge. It has a digital screen that is used to display values and for adjusting them, a measuring head and a number of brackets or jaws of different sizes ranging from 5-100mm.

The digital screen, measuring head and jaws are connected together and used. Another important aspect to be noted is that the simple radius gauge is used for measurement of small radius objects whereas the digital radius is used for larger radius measurement.