GASCO 34L-413, 50 PPM CARBON MONOXIDE, 10 PPM HYDROGEN SULFIDE, 2.5 % METHANE (50 % LEL), BALANCE AIR (20.9% OXYGEN BALANCE 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