GASCO Precision Calibration Gas 44es-432-15 Mixture 25 ppm H2S, 50 ppm CO, 15% LEL HEX, 12% 02, Balance Nitrogen Contained in a 44L Liter ecosmart Factory Refillable Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA