> Parts coming off the same line are sold with a -M (“this bolt was individually magnaflux tested and can go on an aircraft”) or not (“this part can go on a tra

> Parts coming off the same line are sold with a -M (“this bolt was individually magnaflux tested and can go on an aircraft”) or not (“this part can go on a tractor”). I think most practical engineers would agree that the parts are physically identical. Wait, of course they are identical… unless there is a defect! But that's the point of testing: when you can tolerate 1% defect then you can just sample your production line, but if your “safety demonstration”[1] relies on the fact that no screw is going to fail catastrophically under load because there's a defect, then you have to check them all. It's not “That’s paperwork and an ink stamp as the only difference”, exhaustive testing vs statistical testing. The work needed for the testing process is actual work, it's not about filling the paperwork. [1]: not sure this terminology exists in English, I'm just doing a literal translation of a nuclear Engineering concept I know in French only.