GASCO 34L-413-18 | X05NI79CA3413W6 | Calibration Gas Cylinder: 50 PPM Carbon Monoxide, 50% LEL Methane, 10 PPM Hydrogen Sulfide, 18% 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