[postalrat]

I tear apart medical and other machines to recycle parts. I do often see 3d printed parts inside commercial machines, probably because they are making so few of them and it's more economical to just print a couple specialized parts.

[jdeibele]

How can you tell that they're 3d printed? Because they don't have a part number or the manufacturer's name and logo on them?

I don't have a 3d printer myself so maybe it'd be obvious if I printed some.

[robgibbons]

Most 3D printed parts have a telltale texture resulting from the layer-by-layer deposit of material. The same goes for many milled/CNCed parts bearing evidence of tool marks. Once you've seen and held enough, it's relatively easy to identify whether a given part was printed, cast, milled, lathed, etc.

I say most because there are finishing methods which can largely obscure these details and make it less obvious as to which method produced a given part.

[postalrat]

They had the layer lines you see on FDM prints.