Articles related to GD&T symbol rules and walk-through examples of GD&T Symbols and their uses
The video below is in response to a question that we received on our question line from Jeff. Jeff asked us if concentricity is always equal to half of the runout value. ASME Y14.5 defines...
In this article, we explain the differences between bilateral, unilateral, and unequally disposed tolerances. What is a Tolerance? Tolerances on technical drawings communicate the amount of variation permitted from a target dimension. The allowable variation...
In this question line video, Brandon reviews the differences between the GD&T callouts for circularity, circular runout, and total runout. To examine the differences in these concepts it is helpful to first review the Geometric...
Does Runout or Size Control the Circularity/Form Error in GD&T? (Answer: It Depends) In this article video, we aim to answer how Runout is used to control the form/shape/circularity/cylindricity on a cylinder. It also...
Check out this question brought up about Flatness in our GD&T Fundamentals Course. We get a lot of questions about when flatness can be applied and how datums can be used with this. There are...
A theoretically exact reference point, axis, or plane that other tolerances are measured from. Every controlled feature traces back to one.
Controls exactly where a feature must be located. Uses a circular tolerance zone and works with MMC — the most used symbol in GD&T.
Controls a surface or axis so it runs exactly parallel to a datum. Zero degrees is implied — no basic angle needed.
Defines a 3D tolerance zone around any surface shape. One of the most powerful controls in GD&T for complex or freeform geometry.
Controls surface variation relative to a datum axis as the part rotates. Measured at individual cross-sections — simpler and more common than total runout.
Controls whether the median points of a cylindrical feature share the same axis as a datum. Expensive to inspect — position or runout usually works better.
Controls a surface or axis at exactly 90° to a datum. Squareness has a formal definition in GD&T, and this is it.
Controls the entire surface relative to a datum axis in one sweep. More comprehensive than circular runout — and harder to achieve in production.
Applies when a feature is at its largest allowable size. Can unlock bonus tolerance as the feature departs from MMC — often a significant cost saver.
Applies when a feature is at its smallest allowable size. Used when wall thickness or material retention matters more than fit.
The default condition — tolerance applies regardless of the actual feature size. No bonus tolerance. Stricter, but sometimes exactly what the design needs.
The box that houses a GD&T callout. Every geometric tolerance lives inside one — learning to read it fluently is non-negotiable for GD&T.
Defines a 2D tolerance zone along any curved line or cross-section. Think of it as profile of a surface, but applied one slice at a time.
Controls a surface or axis at an exact angle relative to a datum. Requires a basic angle dimension — it's the orientation call for everything that isn't 0° or 90°.
Controls how straight a line element or axis must be. Can apply to a surface line or to an axis — and the difference matters more than most people realize.
