The problem is adjusting the bearing clearance. You have to hold the cone in place while tightening the lock nut, both of which are inside a thin tube. The two concentric thin wall sockets make this easy.

I've adjusted similar bearings using a small socket on the locknut while holding the cone steady with a small screwdriver blade pushed against it's side. This was a real trial-and-error process and took a lot of tries before I got the adjustment right.