Using an External Link for a Part or Assembly is an option in IRONCAD. In IRONCAD you always start working with the assembly and when/if needed, you can select a part or a sub assembly and save it as a reference (external link) to the active file. This "Top-Down" way of working makes it very fast and easy to use!
Note: Make sure to deselect the Cylinder part before creating the Drawing, to make the Drawing having a link to the newly created Cylinder.ics file and not the Cylinder part within the Stirling Engine.ics (Main Assembly) file. The latter is of course always an option in case you do not want to make use of external links. If you have forgotten to deselect the Cylinder part a question will come up where you can choose Yes, in order to create the drawing from the standalone Cylinder.ics file.