GASCO 900es-437TS-1.1 (52.3% LEL) Calibration Gas, 20 PPM Hydrogen Sulfide, 1.1 % (52.3% LEL) Propane, Balance Nitrogen Contained in a 900 Liter Factory refillable cylinder, For Use with Any and All Gas Detectors, Cylinder Connection CGA 330, Calibration Certificate NIST, Made in the USA