Use the following options to set what happens when you select Surfaces > Round Tool.
Specifies the fillet radius the tool uses when you select edge pairs.
Use Preferences tolerance means the Positional value you set in the Preferences window in the Settings category is used. Positional tolerance is used to determine how close the end points need to be to be considered coincident.
Override lets you enter a new value to override the Positional tolerance value you set in Preferences in the Settings category.
The default is Override.