| Step 1. | Choose Home tab→Solids group→Add list→Thicken. 
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| Step 2. | Select the faces you want to offset to construct the thicken feature. | |
| Step 3. | On the command bar, type or select an offset distance. | |
| Step 4. | Click the arrow to define the side to which you want to offset the faces. | |
| Step 5. | On the Thicken command bar, click Finish. | 
Tip:
Set the Select option on the Thicken command bar to Feature to select a stitched surface in one step.