GASCO Precision Calibration Gas 900es-432-15 Mixture 25 ppm H2S, 50 ppm CO, 15% LEL HEX, 12% 02, Balance Nitrogen Contained in a 900 Liter Factory refillable cylinder, For Use with Any and All Gas Detectors, Cylinder Connection CGA TBD, Calibration Certificate NIST, Made in the USA