In Smart 3D 13.1 as well as recent previous version, many part classes have been updated to reference .NET symbol definitions. These new symbols are used in the 13.1 database seed templates. It is recommended that new projects created with Smart 3D 13.1 utilize the new part class definitions and .NET symbols.
Active projects being upgraded from previous versions should continue to use their existing symbol definitions, as modifying symbol definitions in upgraded catalogs is not recommended. Moving the upgraded catalog to the .NET symbols and running Synchronize Model with Catalog Command will modify and change large amounts of existing modeled objects.
If the new .NET symbols are required in an upgraded project, then the supported workflow is to create a new 13.1 catalog utilizing the .NET symbols and a new empty model, and then use the Model Data Reuse (MDR) Command in the Project Management environment to copy the model from the existing upgraded model into the new 13.1 model.