Originally Posted by AnthonyG
All the hubs I have use a 13 mm cone wrench for the front hub and a 15 mm cone wrench for the rear hub and you usualy only need one of each size...
Need? Yes, but it is a LOT easier if you have two 13s (or whichever size your front hub uses...those are the usual sizes.)
See also
http://sheldonbrown.com/cones
Sheldon "Two In Front, One In Back" Brown