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When you dream of becoming a design engineer, you need to up your game. When you design something, it should deliver the desired performance in the real situation. For this, as design engineer you must be good in your visualization, engineering drawing, strength and properties of materials and how you use GD&T to guide the production engineer as well as the inspection engineer.

If you want to know more about GD&T symbols read preceding blog in the sequence Know GD&T symbols start your design engineering career with a bang! Part-2

GD&T Symbols

We have explored 10 GD&T symbols in our previous two blogs, this will cover the remaining 4 symbols.

Circular Runout

Circular Runout indicates variation in a given reference feature/features with respect to another datum/reference when the part is rotated 360° around the datum/rotational axis. Shafts and spindles mount some parts like gears, pulleys which rotate at high speed. These parts should not create any dynamic imbalance which may reduce efficiency of the whole mechanism and even reduce the life span.

  • Gears, pulleys, hubs, clutch plates which rotate at high speed mounted on Shafts, mandrels or Spindles


Circular Runout is applicable where revolving feature itself is short at its functional length or mounts a component which is short at its thickness. The mounting component may have a fixed location on the shaft or move axially. It is indicated by an arrow with slant of 450. To inspect the component should be held at different location which is a datum feature.

The axis of Ø40 is a datum feature. Accordingly, component should be held at Ø40 with the help of datum simulator which can be an expanding sleeve for Ø40, capable of revolving around horizontal axis. Now feature control frame specifies that if a dial indicator is aligned to the component in slowly revolving state, then it must not indicate variation more than 0.05 mm.

Total Runout

This characteristic is applicable for the revolving feature which is considerably long and mounting some revolving component almost equally long.

  • A double or triple gear
  • A stepped pulley
  • A splined hub


It is indicated by a double arrow symbol where an individual arrow shall have the same specification as that for the circular runout.

It indicates that the total runout of the outer diameter B and the adjoining face C is under discussion. The outer diameter features A and D are the joint datum features. If a dial indicator is aligned on the outer diameter B while component is slowly revolving, then the total variation within all observations must not exceed 0.05 mm. Similarly, if the dial indicator is aligned in the surface C and readings taken at various radial locations, then the total variation within all observations must not exceed 0.1mm

Surface Profile

Very complex surface profiles are created for the purpose of aesthetics, aero-dynamics or for creation of a very complex motion. Variation in these profiles should be controlled to avoid function/fitment problems.


Cams, turbine blades, sheet metal body parts of an automobile, impellers


The symbol for surface profile is inverted semicircle. The surface profile can be defined using number of curvatures, straight or slant lines, mathematical equations etc. Feature control frame indicates that profile PQ can deviation from its true shape by not more than 0.5mm. The mentioned permissible deviation of 0.5 mm shall be understood as the local deviation which must be contained within 0.5mm equally distributed on either side of the true profile.

Profile of a line

It indicates permissible tolerance zone around any line in any feature, usually for curved shape. It specified a tolerance zone on either side of the cross section at any point along the surface.

  • Plate cams
  • Sheet metal templates for copy turning
  • Inspection templates


The characteristic symbol is an inverted semicircle without the diameter base. The interpretation is the same as that for profile of a surface.

How to master GD&T Symbols and standout in the job interview?

Just knowing the theory is not enough. You should practice design of a component assembly or modify a component to improve its functionality. With such practice you will become confident to answer any type of question in the interview. You need to choose a training institute which can equip you with the knowledge and skills that the industry demands for. CADCAMGURU is one of such institutes which focusses on honing the job skills of the candidates with practical exposure of designing or improving design of real mechanical components and assemblies. Choosing the right mentor for training is the first step and first strong step leads to a great career.

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