Modified instruments for the fixation of an electrode for continuous pO2 measurements at the presenting part of the fetus sub partu are presented. A new Polyamid cap screw with a specially designed surface shape in order to keep the cement on the cap is described in detail. This simplified the handling of the electrode during application. Polyamid is resistant against Aceton, a commonly used solving agent for the applied Histoacryl cement. Thus the cap screw is reusable after cleaning.