This Guideline describes the requirements on multicontect connector systems and their realization by a six pin plug. They are directed towards process and labratory applications as well as portable instruments. The guideline applies to in-line analytical measurements in process engineering and considers particularly areas with high demands on operational reliability and corrosion resistance. It specifies the mechanical and electricel requirements to be met by connector systems for electrochemical sensors such as pH and redox electrodes, conductivity probes, potentiometric measurements, and combinations thereof.