MST S WS 30 Au CAT III Stackable Safety Plugs with 2mm Rear Socket. Hirschmann Test and Measurement CAT III safety stackable plugs with a solder connection for cables with a cross section from 0.5mm2 to 1mm2 and a maximum outer diameter including insulation of 2.9mm. These stackable plugs feature a spring loaded plug and a unsprung 2mm rear socket for onward connectivity in a wide range of colours. CAT III Spring loaded pin and unsprung 2mm rearsocket Rated at 1000 VAC/DC Current rating 10A Contact resistance 2m