GASCO 34L-450, 100 PPM Carbon Monoxide 50% LEL Methane which is 2.5%, 40 PPM Hydrogen Sulfide 15% Oxygen in 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