Create and use subcategories to control the visibility and graphics of discrete geometry within a category of model elements.
For more information on their use, see 
  About Subcategories for Object Styles.
- Click Manage tab
Settings panel
 Object Styles. 
 
- Click the Model Objects, Annotation Objects, or Imported Objects tab. 
 
- In the Object Styles dialog under Modify Subcategories, click New. 
 
- In the New Subcategory dialog, enter a name. 
 
- Select the Category for Subcategory of. 
 
- Click OK.