A cage with a fastening system (1) in a magnetic resonance device (MRD) is disclosed, said cage in an MRD comprising (a) M pole pieces (45) (M≥2); (b) N side magnets (20) (N≥2), said side magnets substantially enclosing said pole pieces and thereby defining a magnetic envelope and enclosed volume therein; (c) N side walls (10), said side walls substantially enclosing said side magnets; (d) P face walls (30) (P≥2); and (e) a plurality of fastening rods (100); wherein each of said fastening rods physically interconnects at least one pair of side walls, passing through at least one of said side magnets and at least one of said pole pieces.