Page 111 - CITS - Fitter - Trade Theory

FITTER - CITS

Limit Gauges: -
Faster checking of the product is within the specified limits. Less dependence on operator skill and getting affected
by operator judgement. Gauges are economical when compared to measuring instruments

- Plug gauges Types of cylindrical: -
• Double-ended plug gauge: -
A plug gauge, also known as a pin gauge or a GO gauge, is a cylindrical tool used to check the diameter and
depth of a hole or a bore. It consists of a smooth cylindrical rod with precise dimensions. Plug gauges are typically
made to tolerance standards and come in various sizes to match different hole diameters.
To use a plug gauge, you insert it into the hole or bore being measured. If the hole is within tolerance and properly
sized, the plug gauge should fit snugly without any play. If the hole is too small or too large, the plug gauge will
not fit correctly, indicating that the hole is out of tolerance.

Plug gauges are commonly used in manufacturing and machining processes to ensure the accuracy and quality
of drilled or machined holes. They are essential tools for quality control and maintaining tight tolerances in
production.
• Progressive plug gauge: -
Plain cylindrical gauges are used for checking the inside diameter of a straight hole. The ‘Go’ gauge checks the
lower limit of the hole and the ‘No- Go’ gauge checks the upper limit. The plugs are ground and lapped
• Taper plug gauge: -
These gauges made with standard or special tapers are used to check the size of the hole and the accuracy of the
taper. The gauge must slide into the hole for a prescribed depth and fit perfectly. An incorrect taper is evidenced
by a wobble between the plug gauge and the hole.
• Thread plug gauge: -

Internal threads are checked with thread plug gauges of ‘Go’ and `No-Go’ variety which employ the same principle
as cylindrical plug gauges.
- Ring gauges: -

A ring gauge, also known as a ring or snap gauge, is a cylindrical tool used to check the outside diameter of
cylindrical parts, such as shafts or rods. It consists of a fixed or adjustable ring with precise dimensions. Ring
gauges are typically made to tolerance standards and come in various sizes to match different part diameters.
To use a ring gauge, you slide it over the part being measured. If the part’s diameter is within tolerance and
properly sized, the ring gauge should slide smoothly over the part without any play. If the part’s diameter is too
large or too small, the ring gauge will not fit properly, indicating that the part is out of tolerance.
Ring gauges are commonly used in manufacturing and machining processes to ensure the accuracy and quality
of machined parts. They are essential tools for quality control and maintaining tight tolerances in production.
• Plain ring gauge: -
Plain ring gauges are used to check the outside diameter of pieces. Separate gauges are used for checking ‘Go’
and ‘No- Go’ sizes. A `No-Go’ gauge is identified by an annular groove on the knurled surface.
• Taper ring gauges: -
They are used to check both the accuracy and the outside diameter of a taper. Ring gauges often have scribed
lines or a step ground on the small end to indicate the ‘Go’ and ‘No- Go’ dimensions.
• Thread ring gauges: -
These gauges are used to check the accuracy of an external thread. They have a threaded hole in the centre
with three radial slots and a set screw to permit small adjustments.

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CITS : CG & M - Fitter - Lesson 15