GASCO 58es-437TS-1.1 (52.3% LEL) Calibration Gas, 20 PPM Hydrogen Sulfide, 1.1 % (52.3% LEL) Propane, Balance Nitrogen Contained in a 58L 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