GASCO 58L-412: 50 PPM Carbon Monoxide 50% LEL Methane [2.5% by Volume] 25 PPM Hydrogen Sulfide Balance Air [20.9% Oxygen in Nitrogen] contained in a 58 Liter Aluminum Cylinder, Cylinder connection C-10 5/8"-18 UNF, Calibration Certificate NIST, Made in the USA