property Thumbnail.Borders as String
Specifies the size of the borders when the thumbnail is displayed.

TypeDescription
String A String expression that specifies a list of size for margins where the thumbnail picture is displayed. The first number indicates the size of the left margin, the second number indicates the size of the top margin, the third number indicates the size of the right margin, and the last number indicates the size of the bottom margin. All these numbers indicate pixels.  The list is separated by space characters.
By default, the Borders property is "4 4 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