GD&T Spec Table
Geometric Dimensioning & Tolerancing (GD&T) precisely defines form, orientation, location, and runout errors relative to datums. It controls shape accuracy that cannot be expressed through dimensional tolerances alone — essential for functional assurance. Correct specification of straightness, flatness, perpendicularity, and position per KS A ISO 1101 significantly improves assembly quality.
Form Tolerance
Form Tolerance · 6 sizes
Orientation Tolerance
Orientation Tolerance · 3 sizes
Position Tolerance
Position Tolerance · 4 sizes
Runout Tolerance
Runout Tolerance · 2 sizes
Frequently Asked Questions
Why is GD&T (geometric dimensioning and tolerancing) necessary?
Dimensional tolerances alone cannot control form errors like straightness, circularity, and position. GD&T specifies the geometric accuracy required for function, improving quality and reducing defects.
What is a datum in GD&T?
A datum is a theoretically exact point, line, or plane used as a reference for geometric tolerances. Setting datum A as the reference plane lets you measure parallelism and perpendicularity from A. Datums are prioritized A, B, C.
What is the difference between position tolerance and concentricity?
Position tolerance controls deviation of a hole or pin center from its true position relative to a datum. Concentricity controls how closely two cylinder axes coincide. Position tolerance is more commonly used.