GASCO 10L-402E Calibration Gas, Carbon Monoxide 50 PPM, Methane 1.25%Vol = (50% LEL) Pentane simulant, Hydrogen Sulfide 25 PPM, Oxygen 18%, Balance Nitrogen contained in a 10 Liter Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder connection Built in Aerosal Trigger, Calibration Certificate NIST, Made in the USA