This collection of three tools allows you to save the currently selected mesh region for later use, either in the Meshmix tool, or in the Stamp tool.
Use the drop-down menu to select a Hole Fill type: Membrane, COILS, or RotInvCoord (Rotation Invariant Coordinates). Then adjust Bulge and Scale values if required.
Use the drop-down menu to specify the default combination mode when using this part in the Meshmix tool: Append to Mesh, Create New Object, Boolean Union, Boolean Subtract, or No Preference.
The Maintain Dimensions selection forces the object to have the same dimensions as in your current scene when it is used in the Meshmix tool, regardless of the dimensions of the scene into which it will be dropped.