Flattest possible fastener for keychain?

[fredk]

2 hours ago, fredk said:

Its aim to stop people stealing the carts

Here is definitely this

[Klara]

Can't be that because if you really want or need a cart, you pay the Euro, Pound or whatever. Since they mostly cost over a hundred Euros when bought new.

(It's that example that makes me ask in places with a deposit on beakers whether it's ok to keep it. For people in other parts of the world: Germany and France (and probably others, but I stick to what I know) try to reduce plastic waste and at events where you'd have gotten your drink in a disposable plastic cup, you nowadays get a reuseable one which you are supposed to take back to the counter and they'll return the deposit. Except sometimes the cups/beakers/whatever have really nice pictures printed on them and make useful souvenirs and so people keep them. Which at 1 Euro per plastic cup is ok, as far as I've asked... At the soup festival it even was ceramic cups, but for 2 Euros I believe. A potter must have gotten rid of her overstock...)

Edited 5 hours ago by Klara
Info added