I was traveling quite often by airplane within Europe carrying a larger metal object in my hand luggage, a piece of a slackline set to be more precise (approx. 1 kg, 20 cm in length).
I had no trouble at all for about 10 to 15 flights in the past year though it was always checked separately. On two recent flights I was once told I could not carry it at all (Germany) (though the policeman was so nice to let it pass "one last time") and once that I should rather put it in the main luggage (Spain), which I usually don't possess as it costs extra on some budget airlines.
I'm wondering if there are exact regulations regarding metal objects in hand luggage (size, weight, shape), especially for European countries, or if it is essentially is up to the security personnel or police to define it as a potential weapon and forbid it. What can I do to "convince" them that it is sport equipment rather than a dangerous metal piece?