@escapefjrtist is correct. I have a Motorcycle Larry triple clamp on my 2006 too. The bike came with it when I bought it last year. Mine also had a stem nut tapped with the same allen (hex drive) "plug" as the two other spots on the mount. The part I ordered from Ebay is: "RAM-B-236U RAM Mounts B-Size 1-Inch Ball Adapter with 3/8"-16 Threaded Post" from a seller called "synergymounts". See pic below: