The invention relates to a two- or multiple-piece insulating body system (1) for producing medium high voltage cable fittings with a self-locking, electrically insulating closure, for example, for holding cable connections, at least comprising a first insulating body (2) with a linear, bulb-like locking element (3), which is formed on a coupling surface (4) located on the face and which engages in the manner of a snap lock inside a complementary receiving element (6) on the coupling surface (4) of a second insulating body (5), this coupling surface also being located on the face. The insulating bodies (2, 5) forming the electrical insulation of a medium voltage cable fitting each have an inner surface (1.1) pointing toward the cable connection and an outer surface (1.2) pointing toward the surrounding area. At least one insulating body (2 or 5) surrounds the active energized connecting elements, and the linear, bulb-like closed locking element (3), which forms the closure, as well as the complementary receiving element (6) of both insulating bodies (2, 5) to be joined are, in the cross-section, provided in the form of a convex/concave curvature pairing with a head area (7) of the locking element (3), with an opening area (7) of the receiving element (6), with a neck area (8) that can be delimited by the curvature points of inflection and with a shoulder area (9) adjoining the neck area (8).