GASCO 34L-409, 50 PPM Carbon Monoxide 50% LEL Methane 25 PPM Hydrogen Sulfide 12% Oxygen balance Nitrogen, Calibration Gas Mixture, contained in a 34 Liter Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder connection C-10 5/8"-18 UNF, Calibration Certificate NIST, Made in the USA