34es-412 50 PPM Carbon Monoxide 50% LEL Methane 25 PPM Hydrogen Sulfide 20.9% Oxygen in Nitrogen contained in a 34 Liter Factory Refillable ecosmart 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