GASCO 404-17 Calibration Gas, 100 PPM Carbon Monoxide, Methane 2.5% (50% LEL), 25 PPM H2S, 17% Oxygen, 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