To Define a Planar Constraint
1. Click > 
Planar. The Planar Constraint dialog box opens. This dialog box enables you to create a constraint that allows full planar movement, but constrains off-plane displacement.
Planar. The Planar Constraint dialog box opens. This dialog box enables you to create a constraint that allows full planar movement, but constrains off-plane displacement.2. Specify a Name for the constraint. Click the color swatch adjacent to Name if you want to change the color of the icon, the distribution, and the text displayed for the planar constraint.
3. To create a new constraint set, select a constraint set from the Member of Set list, or click New to open the Constraint Sets dialog box.
4. Select the planar surfaces to constrain. You can select the geometry before or after you open the Planar Constraint dialog box. The Surfaces collector displays your selections.
5. Click OK.