I've noticed some stuff people have for sale on there are one purchase, but it will have multiple parts. They aren't even fully connected every time. I have a 4 part item I was going to have printed, and it seems these multiparts in one purchase tend to be cheaper than 4 separate purchases. How do I get one file to have all 4 parts in it? I can save it as a solidworks assembly, but that's not uploadable. I can save it as an .stl file, but that separates them into 4 separate files instead of the one assembly file. How do you guys do it when you have multiple parts? What kind of file do I need to save as?