Chapter-6 Radius Gauge and Feeler Gauge

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.

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.

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.

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 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.

feeler gauge by stanley

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. Advertisements Report this ad

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.

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


On basis of the blades, it is of two types, tapered and parallel.

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. Advertisements Report this ad

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.

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

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