Are snow spikes (like these) allowed in hand luggage when flying?
I brought microspikes (virtually the same as these spikes) in my hand luggage twice in late May this year, on Ryanair STN-BCN and Vueling BCN-LGW flights, for hiking in the Pyrenees. There was no problem each time.
I know OP clarified in a comment that they were asking about Europe, but since the question wasn't tagged "europe" and another answer relating to the TSA received upvotes, I thought I would post my own findings relating to the TSA's stance on snow spikes (a.k.a. crampons).
There is conflicting information on the TSA's web site as to whether crampons are allowed in carry-on bags. One of their blog posts from 2014 says "Crampons are permitted in both carry-on and checked baggage".
However, their undated What Can I Bring page says "No" to carry-on bags and "Yes" to checked bags.
The AskTSA twitter feed seems to clear up the issue, as most of their responses to users since late 2016 have said that "Crampons and micro spikes are allowed in checked bags only".
There does appear to be one exception though. A user asked about Yaktrax style crampons, and the TSA said "crampons without spikes are allowed in carry-on bags".
You will never get a sufficient answer, because the item is too special. The TSA does not have it in their Item-List of Prohibited Items, so you are relying on the personal opinion of the person at the security check. Either you ask TSA via Email and print the mail and hope the best (if they allow it in the Email), or just put them in your checked luggage to avoid confusion, stress and additional time for discussions