Vacuum interrupter with one movable contact

A vacuum interrupter, comprising:

• one movable contact fixed on a movable contact stem, the movable contact stem having external spanner flats;
• and
• one fixed contact with a fixed contact stem,
• wherein the fixed contact and the movable contact are located in an electrically insulating tube, which is vacuumtightly closed by metal lids at both sides,
• wherein the fixed contact stem is placed vacuumtightly on a first of the metal lids, and the movable contact stem is guided through an opening of a second of the metal lids via an axially extendable vacuumtight bellows,
• wherein, in order to create a twist protection of the movable contact stem, a ring disc shaped plastic part with a central opening, through which the movable contact stem is guided, and inner spanner flats inside the central opening, is connected externally to the vacuum interrupter such that the inner spanner flats complementarily fit closely to the external spanner flats of the movable contact stem,
• wherein the plastic part is fixed to the second metal lid,
• wherein the plastic part is fixed in an angular position to the second metal lid by a self tapping screw,
• wherein an inner diameter of the opening of the second metal lid and an outer diameter of the movable contact stem are dimensioned so as to form a circular ring slot, and
• wherein the self tapping screw is screwed into the circular ring slot at an arbitrary angularity.