Form controls are used to control the form or shape of a feature and in some cases the axis or centerplane of a feature. Form controls define how much a part’s actual shape can vary from its perfect or ideal shape. There are four form controls: straightness (u), flatness (c), circularity (e) and cylindricity (g). Form controls only apply to individual features and are not related to datums.
GD&T GEOMETRIC CHARACTERISTIC SYMBOLS
| Tolerance Type | Characteristic | Symbol | |
|---|---|---|---|
| For individual features | Form | Straightness | u |
| Flatness | c | ||
| Circularity | e | ||
| Cylindricity | g |