Crazy. It comes with an Allen key, but the instructions don't mention how to use it or what it's for. The lock nut looks like you could use a wrench on it and I'm assuming you can. The two holes in the lock nut fit a hex wrench. You insert the hex key with the short side in, hold the locking knob on the top of the angle grinder (on the other side of the wheel), and then turn the hex key clockwise to tighten it. On the contrary, to weaken. Reading the description I thought the grinder came with a 5/8 nut to be used with a regular wrench as they don't mention that the wrench is a hex wrench. The instructions and product description could be more informative. . Otherwise this is a good angle grinder. Boring tool that does the job.