R.J.VON Backrest Carrier Plate Base is for Honda SP 125 fitting adding surface area so that your Top plate is mounting kit allows you to securely attach your Bike Top Case to the Rider luggage rack. The mounts and hardware included in the kit attach to the luggage rack through the pre-drilled mounting points already measured to the specifications on the rack. The hardware and mounts are very slim and unobtrusive when the top case is not attached to the rack so you don't have to worry about the kit interfering with your strapped down gear.