GASCO 34L-428-20: 60 PPM Carbon Monoxide, 1.45% Volume (58% LEL Pentane Simulant) Methane, 20 PPM Hydrogen Sulfide, 15.0% Oxygen, Balance Nitrogen 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