Creating 3D Geometry - AutoCAD 2011 and AutoCAD LT 2011: No Experience Required - page 864

FiGuRE 16.38 Selecting the box from the Subtract Boolean operation
NOTE the object that you are editing is the window frame and the
operand is the subobject. You must hold down the Ctrl key when selecting a
subobject to expose its grips.
4. Click one of the triangular grips that control the width of the box,
drag it to make the box wider, and then enter 12 ↵ ( 305 ↵ ) to stretch
the box 12 ″ (305 mm) in the X direction, as shown in Figure 16.39.
FiGuRE 16.39 Adjusting the size of the window frame
The side of the window frame is now much wider than the other
edges of the frame. You can fix this by adjusting the size of the box
operand.