Gasco Custom Mixture | 5000 Hydrogen (H2) 5000 Ethylene (C2H4) 5000 Carbon Monoxide (CO) 5000 Carbon Dioxide (CO2) 5000 Oxygen (O2) Balance Nitrogen 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