ComClass is used by the class manager's GetFactoryFromClass method. This method checks the ComClass of each class factory on the server, against the class passed to it, in order to return the class factory that creates objects of that type. It is also used by the CreateComObject method to create the correct COM class. 

ComClass is initialized, in the class factory constructor, to the COM class type that is passed to the constructor. 

Create 

CreateComObject 

GetFactoryFromClass