Choose Home tab→Modify group→Offset Faces 
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Select the faces you want to offset, then click the Accept button.
Note:
Hole feature faces cannot be selected for offset.
Type the offset distance on the command bar.
In the graphic window, use the cursor to define the offset direction.
Finish the feature.
Tip:
You can use the Select option on the command bar to specify whether you want to offset individual faces you select, a tangentially continuous set of faces, a set of faces that belong to an existing feature, or an entire body.
The faces are offset using the surface normal of the faces you selected.
You can also select a keypoint to define the offset distance. When you select a keypoint, you must select a reference face to define the offset direction. The reference face must be one of the faces you selected to offset.