In the next section, we allow Autodesk Inventor to place a plane in the middle of the part. This technique is useful because it does not require any dimensions or edits to maintain the position. If the width of the part is edited, the plane stays centered.
We will then create an offset work plane to use as the location of a new sketched feature.
Select Midplane between Two Parallel Planes from the Plane drop-down menu. To create a work plane that bisects the part, pick the face with the new feature and then the parallel face on the opposite side of the part. A work plane is created in the middle of the part. 
Start the Mirror command. Select the extrusion, the fillet, and the through hole as the features to mirror. 

Select Offset from Plane from the Plane drop-down menu. Steps 4-6 create a work plane that is parallel to the center plane and offset a specific distance.

Start a new sketch on the offset work plane. (Select the edge of the work plane and click Create Sketch from the contextual mini-toolbar.)
Start the Project Geometry command. Select the front edge as shown to project it to the sketch plane, and then sketch and dimension the profile shown. Be sure to select the bottom edge of the part when creating the 25 mm dimension. 
Finish the sketch.
Extrude the profile 14 mm towards the interior of the part. Use the Direction 2 button on the mini-toolbar to change the orientation before selecting OK. 
Start the Hole command.
Start the Mirror command. Select the extrusion and the through-hole as the features to mirror. Select the work plane in the center of the part to satisfy the Mirror Plane pick. 
We now create two chamfers on the front of the base to create a smaller footprint for the front of the base. To determine the chamfer distance, we use the Measure Distance command to extract the distance between the two planes.
Start the Measure Distance command. You will find this command in the marking menu, or on the Measure panel of the Tools tab. Select the plane on the outside of the part and the plane on the front face of the small mounting tab. The distance between the two faces displays as 13 mm. We will use this distance to create a chamfer that terminates at the edge of this feature and the edge of the mirrored copy. 
Start the Chamfer command. Select the Two Distances option from the fly-out button on the mini-toolbar. 

In the next exercise, we create a tapped hole for a set screw on a curved face. To do this, we create a work plane that is tangent to the curve and parallel to the base.