You have to import it into Inventor in STP 219 format and in the import options de remove the flag in divide periodic faces otherwise all the faces, cylindrical solids will be divided into 2. If the geometry is simple you can choose ACIS which was the modeling engine up to Inventor 6. Then he bought the ACIS source codes, today from solidworks dassault systemes, and developed it as Autodesk shape manager, but the base still remains that. Greetings from Luigi, former Autodesk technician and Solidworks