Offset Constraints 

When defining an offset-type constraint between planar elements, you need to specify how faces should be oriented.
The offset value is always displayed next to the offset constraint.
  The unit used is the unit displayed in the Units tab of the Tools > Options dialog box. If you wish, you can customize it.
  The following table shows the elements you can select for defining an offset constraint.
 
  Point Line Plane
Point
Line
Plane
 
  • NA: Not Applicable.
  • Point: a point, a sphere center, a cone vertex for example.
  • Line: a line, a cylinder axis, a cone axis for example.
  • Plane: a plane or a planar surface for example.
 

Positive and Negative Offsets
  When setting an offset constraint, you can define positive or negative offset values. For this, remember that:
 
  • At least one of the components to be constrained must be a planar element, otherwise you cannot set positive nor negative offset values.
  • The vector normal to the planar element indicates the positive offset value.
  • If the planar element is an oriented plane, the normal vector pointing to the side opposite to material indicates the positive value.
  • If the planar element is a wireframe plane, the application automatically deduces the positive or negative value. Green arrows show the positive value.
 
 

  • If both components are planar elements, the selection order of the elements affects the result when using the orientation option (Same, Opposite, Undefined). The normal to the first selected element gives the positive value.