property Thumbnail.Margins as String
Specifies the distance between thumbnails, when multiple thumbnails are displayed on the control.

TypeDescription
String A String expression that specifies the distance between thumbnails, when multiple thumbnails are displayed on the control.
By default, the Margins property is "4 4". Use the Alignment property to specify the caption being displayed on the thumbnail control. Use the Transparency property to specify the percent of transparency being used to paint the caption on the thumbnail. Use the Appearance property to specify whether the thumbnail displays a border.

You can use the following properties to define the distance and padding of the thumbnails