No other size wrench will work, but any type of adjustable wrench will do for the locking nut. [title] Put the flat wrench on the bearing cone between the hub and the locking nut.
[header] How to grease bicycle wheel bearings [title] Get some good, flat, open wrenches. [step] Make sure they are in sizes 13 mm and 15 mm. Those are the most common sizes.