ELI5 3D Printing - Does NASA really email tools to space?

How does NASA effectively email physical tools and equipment to astronauts on the Space Station? If you 3D print a vinyl record from an MP3 file, is the music digital or analog? How exactly does 3D printing work like a computer-controlled hot glue gun? Why is 3D printing a game-changer for prosthetic limbs? Why can't 3D printers replace traditional factory assembly lines for mass-producing everyday items?

... we explain like I'm five

Thank you to the r/explainlikeimfive community and in particular the following users whose questions and comments formed the basis of this discussion: genelatifah, fyre2387, flamedieout, dkf295, mroctantis, atrain82187, t0m0hawk and nola-kola

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