Abstract: A device for fixing and maintaining coils contained within armatures to provide a constant and homogeneous magnetic field. The device includes an amagnetic bench having a longitudinal axis, a frame having two upstanding panels mounted on the bench, a first reference armature secured by the panels, at least two additional armatures for support longitudinally along the bench, each of the additional armatures being of a diameter less than or equal to that of the first armature, and mounting apparatus for supporting the additional armatures at locations on the bench spaced from the first armature, whereby the additional armatures may be placed, relative to one another and to the first armature on the periphery of an imaginary sphere. The mounting apparatus includes adjustment apparatus for adjusting the additional armatures relative to the first armature in longitudinal and vertical directions.