Use this page to adjust the options for the STL file reader. 
-  
Default Units 
 
-  
Specifies the type of units 
  Autodesk Navisworks uses when opening STL files. 
 
Tip: If the chosen unit type turns out to be wrong, you can rescale the model by using the 
  Units and Transform option. (Right-click in the 
  Scene View, and click 
  Units and Transform on the context menu.