Form
Straightness
Keeps a line element or feature axis from bending too far.
A clear GD&T reference
Read the callout.
Understand the part.
A visual, plain-English guide to geometric dimensioning and tolerancing for engineers, machinists, inspectors, and curious beginners.
The symbol library
Every essential control,
without the mystery.
Choose a symbol to see what it controls, whether it needs a datum, and how to read a real-world callout.
Form
Flatness
Keeps an entire surface between two perfectly parallel planes.
Form
Circularity
Keeps every circular cross-section of a feature acceptably round.
Form
Cylindricity
Controls the complete shape of a cylindrical surface in one callout.
Profile
Profile of a Line
Controls a 2D cross-section of a curved or irregular feature.
Profile
Profile of a Surface
Controls a complete 3D surface against its true shape.
Orientation
Angularity
Holds a surface or axis at an exact basic angle to a datum.
Orientation
Perpendicularity
Keeps a surface or axis square to a datum.
Orientation
Parallelism
Keeps a surface or axis parallel to a datum reference.
Location
Position
Locates a feature precisely using a tolerance zone and datums.
Runout
Circular Runout
Limits surface variation at each circular slice as a part rotates.
Runout
Total Runout
Controls an entire rotating surface relative to a datum axis.
Location
Concentricity
A legacy control for keeping derived median points centered on a datum axis.
Location
Symmetry
A legacy control for keeping derived median points centered about a datum center plane.
A simple way to read GD&T
Start with the box.
Every feature control frame communicates the same core ideas. Learn those once, then any drawing gets easier to read.
Find the symbol
It tells you what type of geometric requirement is being controlled.
Read the tolerance
It tells you the size and shape of the allowed tolerance zone.
Follow the datums
They establish the reference system used to orient or locate the part.
Desk-ready learning
Keep the controls
within reach.
Printable GD&T references and shop-floor charts are on their way. Designed to be useful from first article to final inspection.
Preview the print shop →