A rotary knob for an electrical system includes a body containing a rotary maneuvering member which actuates a cam-driving part and bears one or more electrical units. A cup is defined between an outer cylindrical flange of the body and an inner cylindrical sleeve, and contains a spring either of a helical type for urging a sliding ring separate from the driving part, or of a torsion type to return the maneuvering member. The ring provides a sensitivity function. The cylindrical sleeve defines in a central opening thereof a centering seat of the shank of the maneuvering member.
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