Extent may have a value between 0 and 500. It is not strictly a margin, since labels are rendered in area created by an Extent. Setting the Extent to too small a value will result in labels for that axis appearing clipped.
Extent is ignored for the axes of 3D charts, it applies to 2D charts only.
Target Platforms: Windows 10, Windows 8.1, Windows 8, Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2