GASCO 421-CO2 Calibration Gas, 100 PPM Carbon Monoxide, 5000 PPM CO2 [0.5%] 50% LEL Methane, 25 PPM H2S, 18% Oxygen, Balance Nitrogen contained in a 34 Liter Disposable Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA