GASCO Calibration Gas 34L-403S Mixture 50 PPM Carbon Monoxide, 25 PPM Hydrogen Sulfide, 1.62 % Methane, (32.4 % LEL), (50 % LEL Propane Equivalent), 19 % Oxygen, Balance Nitrogen, contained in a 34 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