M3550RK-BX - Service-PackInstallation Mounting Kit Powder Coated X-Black with Hardware, Front Rubber Seal and Endgate Seal Mount Application.

Clamp Style, Clamp-On Mounting Kit is designed for Mounting Cross and Saddle Boxes with Clamp-On Style Mounts. One Bolt per Clamp and two to three Clamps per side can be used to Mount Box to Truck Rail. Kit comes with Bolts, Washers, Mounting Clamps, Nuts, Rubber and Installation Sheet. 

Installation Sheet: http://www.truckbox.com/images/PDFI/ISL2500.pdf 

Description Sheet: www.truckbox.com/images/PDF24/C-Page 84.pdf