You must indicate in your application form the articles in respect of which you wish to register your design and must list the articles in the class or classes they fall into as well as the number of class they fall into. The International Classification for Industrial Designs (“the Locarno Classification”) will guide you how to find out the classes that your articles fall into. There are 32 classes under the Locarno Classification.
Some examples of classes under the Locarno Classification can be viewed here. (Source: WIPO)
All the designs classes can be viewed here.