This is a set of two Blue Aluminum 23mm Hex Hubs for the Team Losi LST2.  These are made by CEN Racing, and they will also work on the CEN Genesis, Nemesis, and GST trucks.  The 23mm hex size is used in many popular wheels, like many of those by Pro-Line.  The larger hub makes it stronger, and the wheels are less likely to break as well.  If you need a full set of four, purchase a quantity of "2" sets of these.