GASCO 58L-403E GASCO 50 PPM Carbon Monoxide, 25 PPM Hydrogen Sulfide, 1.62 % Methane, (32.4 % LEL) , (50 % LEL Propane Equivalent) , 18 % Oxygen, Balance Nitrogen contained in a 58 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