Industrial Scientific 18109158 equivalent made by Gasco 100PPM CARBON MONOXIDE, 25PPM HYDROGEN SULFIDE, 18% OXYGEN, 2.5% METHANE contained in a 116 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