A passenger wil encounter two security scans in the Dublin airport when flying to the United States.
During the first, on the "Irish side," the staff noticed a pack of sewing needles, and asked to inspect the small backpack that I was using as carry-on. The guy allowed me to continue onward, but when I told him I'd be switching planes in Chicago, he suggested that I might save myself the trouble and get rid of the needles, which I hadn't even remembered packing. So I figured I'd do that in Chicago. Then, to my surprise, even after having "pre-boarded" at U.S. customs, there was another, more stone-faced and no-nonsense American baggage scan. They didn't catch the sewing needles. They did ask everybody to submit their shoes for x-ray.
It wasn't until transferring in Chicago that I passed through the infamous "backscatter" body-scan. It was either that or let some guy feel around my body. I wasn't in the mood to stage a protest and so I assented to the violation of personal liberty.
At home in Central Oregon, I was making sure I'd unpacked everything when I first discovered the weapons-grade component of the backpack I'd carried through nine countries over a period of 11 years.
Tucked into a sleeve along the middle of the back was a removable stiffener, a thin one-inch-wide curved bar of aluminum that would flatten out to about two feet long.
This bar, while only 3/16-inch thick and only aluminum, could of course be sharpened could be used as a weapon. And, at basis of this problem, this is a bar of metal never mind what kind of metal it is.
I was able to carry a bar of metal to America on a transcontinental flight where shoes were scanned, bottles of liquid confiscated, and a pack of needles under suspicion.