Yes, you’re right. This morning I checked online size of a nickle which is 21,21mm (diameter) and 1,95 (thickness) while 50 euro cent coin is 24,25mm in diameter and 2,38 in thickness. Material of these coins is “nordic gold”, a type of brass. I always use that coin in tests like this but it maybe would be better with a 20 cent coin because it’s much similar to a nickle, talking about dimension..