As I have mentioned in previous posts, in retirement I have become a student again. In a seriously great deal, Wisconsin says that once you hit 60 tuition at both the university system and the technical college system is free. Just a "thank you" for paying taxes all those years.
So I study course catalogs and if something interests me I sign up.
This fall I am doing just one class, an intro to mechanical design.
It is interesting. One of our early projects was to retro engineer a lego. Get out the calipers, do careful measuring, draft it up in Solidworks and toss it on the 3D printer.
In this view it is hard to tell the original from the "knock off"
But the close up tells the tale. Note the rougher surface on the example that was 3D printed. Note also please that they fit together perfectly.