Restrain Normal
The Restrain Normal 
option is used to apply restraints normal to a boundary.
The nodes will be restrained in the direction perpendicular to the boundary, and free to move tangential to the boundary.
Nodes restrained in the normal direction are indicated by a roller symbol with a line perpendicular to the boundary, when Restraints are displayed as configured in the Display Options dialog.
See the Applying Restraints topic for information about applying restraints.