This window, available only for Gap contact, lets you set the index range of a structured Part that will be checked for interactions. This option is not available for unstructured parts.
For Trajectory contact and for unstructured parts the Interaction by Group option can be used instead to select only a region of a Part for interaction.
Select the Part for which you want to set the index range for interactions in this box.
Enter the index range that you want to be checked for interaction.