GASCO 34ls-303E Calibration Gas Mixture, Carbon Monoxide 50 PPM, Methane 1.62% = (50% LEL) Propane simulant, Oxygen 18%, Balance N2 contained in a 34 Liter Disposable Steel Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection CGA 600, Calibration Certificate NIST, Made in the USA