Nolab | F105325PM51 | equivalent by Gasco | 50 PPM Carbon Monoxide | 50% LEL Methane [2.5% by Volume] | 25 PPM Hydrogen Sulfide | 12% Oxygen | balance Nitrogen, Calibration Gas Mixture, 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