box.urdf

<robot name="box">
    <link name="world"/>
    <gazebo reference="world">
        <static>true</static>
    </gazebo>
    <joint name="fixed" type="fixed">
        <parent link="world"/>
        <child link="real_box"/>
    </joint>
    <link name="real_box">
        <inertial>
            <origin xyz="0.45 -0.2 0.0" />
            <mass value="1.0" />
            <inertia ixx="0.0" ixy="0.0" ixz="0.0" iyy="0.0" iyz="0.0" izz="0.0" />
        </inertial>
        <visual>
            <origin xyz="0.45 -0.2 0.0"/>
            <geometry>
                <box size="0.4 0.1 0.3" />
            </geometry>
        </visual>
        <collision>
            <origin xyz="0.45 -0.2 0.0"/>
            <geometry>
                <box size="0.4 0.1 0.3" />
            </geometry>
        </collision>
    </link>
</robot>