RKI 81-0161RK-02 equivalent by GASCO 100 PPM Carbon Monoxide 50% LEL Methane (2.5% by Volume) 25 PPM Hydrogen Sulfide 18% Oxygen in Nitrogen contained in a 58 Liter Aluminum Cylinder, Cylinder connection C-10 5/8"-18 UNF, Calibration Certificate NIST, Made in the USA