Hi Igor,
It sounds like you are looking at the connectors. A rod connector is infact a CBAR element, but a bolt connect is a series of Rod and Beam elements that can be used to represent a bolt, it tends to be much more efficient then including a solid modeled bolt. Beams can be generated by associating a line element physical property with a sketch line generated in Inventor or Solidworks. Line elements can be either bar, beam, or pipe elements.
Andrew Sartorelli - Autodesk GmbH