GASCO 10L-413-18 Calibration Gas Mixture, 50 PPM Carbon Monoxide, 50% LEL Methane, 10 PPM Hydrogen Sulfide, 18% Oxygen, in Nitrogen contained in a 10 Liter Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder connection Built in Aerosol Trigger, Calibration Certificate NIST, Made in the USA