GASCO 34LS-301A, 50% LEL Methane [2.5% Methane] 50 ppm Carbon Monoxide, 18% Oxygen, Balance Nitrogen, Calibration Gas, 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