After running the engine for about 5 minutes, the belt will stretch. You need to check the tensioner AFTER the belt stretches. 

If you can't find a belt within your range with a Gates belt, you need to cross reference the Part Number. Different brands will stretch differently. You CAN NOT go buy the same length belt from different brands and expect them to function the same after the belt has stretched. 

Gates Belts can be found at your local O'Reilly's.

Belt Listings Organized by Numbers of Ribs: