Contact assembly for selector of step transformer

In combination with a step-transformer drum formed with throughgoing apertures each centered on a respective axis, a contact assembly in each aperture comprising:

• an insulating washer lining the aperture and having an inside part lying on an inside surface of the drum and an outside part lying on an outside surface of the drum;
• a stud having an enlarged head bearing outward on the inside washer part and a shaft projecting through the washer past the outside washer part and formed outside the outside washer part with a transversely throughgoing hole;
• a pin projecting transversely through the hole;
• and
• structure forming an outwardly directed ramp on which the pin bears inwardly, whereby rotation of the stud and pin in one direction relative to the structure makes the pin travel along the ramp and tightens the stud in the aperture and opposite relative rotation loosens the stud.