The Helmholtz coils are used to create magnetic fields for deflecting electron beams and are attached to the tube holder D (1008507). The tube holder allows the coils to be set up in Helmholtz configuration to generate a highly uniform magnetic field perpendicular to the axis of the tube.
 

The two air-filled coils are made of lacquered copper wire on a plastic bobbin on an insulating stand rod with plastic sleeves for insertion into specially drilled holes on the demonstration tube holder. Connections are labelled from the start (A) to the end (Z) of the coil winding.