Place fabrication parts for the selected service.
Video: Creating an MEP Fabrication Layout in Revit
When you click the arrow, a drop-list displays additional parts based on the size. This drop-list is controlled by the conditions in the service definition, similar to routing preferences. For example, a bend may use a pressed bend up to a certain size, and a segmented bend above that size.
This indicates that the fabrication part (ITM) is not currently supported in Revit MEP. These include components such as flex duct, structural members, air terminals, and mechanical equipment. In place of these components, you can use Revit Family (RFA) based components using the category's standard placement tools.