I had an assembly to start. I saved that as a part. I then deleted all my internal parts. I created bosses/extrudes/revolves to make my part become a block. I started with about 50 solid bodies (NO SURFACES). Then got down to only 3 Solid bodies and saved the part as a STEP file. When I open the STEP file, all of the internal features I created is missing, its completely shelled out and now I have 3,500 surface bodies. I don't understand what its doing.. Cant I save a solid part as a STEP and the STEP file opens my solid part?