GCO0046 CROWCON Calibration Gas Mixture Equivalent by GASCO, 50% LEL Methane, 250 PPM Carbon Monoxide, 15 PPM Hydrogen Sulfide, 18% Oxygen, Balance Nitrogen, contained in a 58 Liter Disposable Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA