This is an adapter plate from RIXEN&KAUL. It is a new, unused item. Originally for RIXEN&KAUL baskets, it has a part that can be attached to the mount, and a back plate to sandwich the basket, securing it with 4 bolts and nuts. By attaching this to your favorite bag, you can create an original bag that can be mounted on RIXEN&KAUL mounts, even if it's not a RIXEN&KAUL basket. I believe this item is not currently available in Japan.