Same here... Diazed fuses are keyed by rings with different inner diameters screwed into the base, preventing the use of fuses with thicker tips. However, a) the rings are porcelaine and thus fairly easy to destroy with brute force and b) they aren't exactly tamperproof or irremovable, they just screw in. They do require a special key, but that is easily substituted with two flat blad screwdrivers. Besides, both keys and rings of all sizes are sold in every DIY store. Every time I find one of those keys in a fuse box I immediately get suspicious (even though there were legit reasons to use one, at some point even 1.5mm2 wires that can be fused 10A (16A in Germany) by today's standards were only fused 6A, similarly with larger wires).
