Holding a pickaxe / axe / shovel head on its own, it's possible to use this for mining without assembling a full tool with a handle. This gives infinite durability.

It seems I have forgotten to check if the item which carries the properties is an actual tool. Does the parts have differing mining speeds, or is there only the fact that it can be used to mine?

The mining speed + mining level seems to match the type of tool head.

Alright, then I know what is wrong, it should be an easy fix.

LMAO