Use Rectangle to create square and rectangular splines.

Examples of rectangles
Procedure
To create a rectangle:
- Go to the
Create panel and turn on
(Shapes).
- Click Rectangle.
- Choose a creation method.
- Drag in a viewport to create a rectangle.
Optionally, press Ctrl while dragging to constrain the spline to a square.
Interface
Rendering and Interpolation rollouts
Most spline-based shapes share these parameters. For details, see Rendering rollout and Interpolation rollout.
Creation Method rollout
The Rectangle shape offers the standard creation-method choice: Center or Edge. For details, see Creation Method rollout.
Keyboard Entry rollout
Creates a Rectangle spline from the keyboard. Use the X/Y/Z settings to specify the center point, and the remaining parameters to specify the dimensions and corner radius, then click Create. After creating the spline, you can use the Parameters rollout controls to adjust its settings (see following).
Parameters rollout

Once you have created a Rectangle spline, you can make changes using the following parameters:
- Length
-
Specifies the size of the rectangle along the local Y axis.
- Width
-
Specifies the size of the rectangle along the local X axis.
- Corner Radius
-
Creates rounded corners. When set to 0, the rectangle contains 90-degree corners.