This checkbox is not shown on the Select Field Assignments page or the Select Data Fields page when importing part data into or exporting part data from a System file or Prediction Parts Library file. This checkbox is shown on any other table for which you can create a custom Table Format file. It does not matter whether you have created such a file, but only that it is possible that you can create it. For example, this checkbox is available when importing or exporting Configurations table data but is unavailable when importing or exporting Maintainability table data.