GASCO 116L-428-20 Calibration Gas Mixture with 60 PPM Carbon Monoxide 1.45% Methane 20 PPM Hydrogen Sulfide 15% Oxygen in Nitrogen contained in a 116 Liter Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder connection C-10 5/8"-18 UNF, Calibration Certificate NIST, Made in the USA