RAE Systems 600-0050-070 Calibration Gas By GASCO 2.5% Volume Methane (50% LEL), 18% Oxygen, 50 ppm Carbon Monoxide, 10 ppm Hydrogen Sulfide, Balance Nitrogen contained in a 58 Liter Aluminum Cylinder, Cylinder connection C-10 5/8"-18 UNF, Calibration Certificate NIST, Made in the USA