The Add Objects Rectangle tool inserts a Rectangle primitive in the Working-Volume at the location of the 3D Cursor.
Rectangle primitives can also be generated with exact dimensions or drawn interactively using the Build > Build Primitives menu.
The Build Primitives Rectangle Tab page enables the generation of Rectangle models by a specified dimension.
Type in the desired Length, Width and Center point, then press the Make button. Note that the Center is the point in the Working-Volume 3D space that the center of the Rectangle is placed.
You can also interactively generate a rectangular primitive by dragging out a bounding box in any of the Working-Volume' TOP, FRONT, or SIDE views. The specified rectangle will fill the space of the bounding box. Note that the Auto checkbox must be checked to interactively draw primitives.