Use this procedure to change one mass element into another, add it to a mass group, and change its size. 
- Double-click a mass element. 
 
- On the Properties palette, expand Basic 
 General.  
- Select a new basic shape for Shape. 
 
-  To attach the mass element to a mass group, select a mass group for Attached to. 
 
- Expand Dimensions. 
 
- Enter new dimension values for the mass element. 
Note: When you change the size of a mass element, the center point remains constant and the change is applied to both sides of the element.