This is a bracket that helps install a newer 2,5" HDD that has a standard hole pattern, on an older computer that has a different hole pattern, usually to accept thicker drives. There are 3 versions, one with holes only at the bottom, and two with holes on the sides at different positions. It is designed so that the mounting screws can be directly inserted into the plastic. It also compensates for the HDD thickness. In my case I used it to install a newer HDD to an Amiga 1200 as seen on the photos.