Block structured hexahedral meshing is required for many applications but remains unreachable in an automatic manner for realistic simulation models. In practice, true industrial cases are handled using complex and rich interactive software, and generating a block structure for a mechanical CAD part can require several days to weeks for an expert engineer. For many years now, several scientific works have demonstrated that 3D frame fields are a very powerful tool for hexahedral meshing. These works remain mainly theoretical and their application is limited to simple 3D models. In this paper, we propose to provide the necessary components to build an interactive tool using frame fields. The principle of the approach is to build a valid dual structure made of 3D dual sheets, which are aligned along a 3D frame field, and then to convert this dual structure into its primal hexahedral block structure.