On Flat Face

You can use this option only when all the selected faces are planar. Each face can be in a different plane. Each face is restrained relative to its own directions (Direction 1, Direction 2, and Normal).

Attribute Value
Possible DOFs for solid meshes 3 translations
Possible DOFs for shell meshes 3 translations and 3 rotations
Possible DOFs for trusses 3 translations
3D symbol
translation rotation
Selectable entities Planar faces only
Translations

Along face direction 1

Along face direction 2

Normal to face
Rotations (for shells only)

About face direction 1

About face direction 2

About normal to face

Example

 
The selected flat face (shown in yellow) can only slide along in the direction shown by dashed red arrows, for example, Dir 1 of the face. Setting the other two directions (Dir 2 and Normal) to zero enforces this condition.
 
The selected flat face (shown in yellow) can slide along Face Dir 1 and Face Dir 2. Setting the normal motion to zero enforces this condition.
The desk shown above is free to move on the ground (dashed red arrows) and no normal motion (solid blue arrow) is allowed. The selected flat faces (shown in yellow) can slide freely along Dir 1 and Dir 2 of the selected faces and restrained in the Normal direction.
The inner slider is free to slide along the directions shown in dash arrows. Use the On flat face restraint type to specify zero displacements along Face Dir 2 and Normal to the face.