On the command bar, click the Planar Align button on the Relationship Types list.
Do one of the following:
If you are replacing a relationship you deleted from an existing part, select the part to be repositioned.
If you are placing a new part into an assembly, select the planar face to be aligned.
Select a part in the assembly.
On the part in the assembly, select the planar face to which the first part is to be aligned.
Press Enter.
Tip:
When you apply a planar align relationship, the faces are forced to face the same direction.
You can apply the planar align relationship with a floating offset or a fixed offset.
For a fixed offset, type an offset value on the Place Part command bar in the Offset Value box. You can change the offset value later.
For a floating offset, you can apply an additional relationship to control the offset value.
You can use the Flip option on the command bar to change the planar align relationship to a mate relationship.