GASCO 900ES-428-20 Calibration Gas Carbon Monoxide 60 PPM, Methane 1.45%Vol = (58% LEL) Pentane simulant, Hydrogen Sulfide 20 PPM, Oxygen 15%, Balance Nitrogen contained in a 900 Liter Factory refillable cylinder, For Use with Any and All Gas Detectors, Cylinder Connection CGA 330, Calibration Certificate NIST, Made in the USA