GASCO 416 Calibration Gas, 200 PPM Carbon Monoxide, 20 PPM H2S, 2.5% Methane (50% LEL) 18% 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