GASCO Precision Calibration Gas 34es-428X-20 Mixture 20 PPM Hydrogen Sulfide, 1.45 % Methane,(29 % LEL,(58 % LEL Pentane Equivalent), 15% Oxygen, Balance Nitrogen contained in a 34 Liter Factory Refillable ecosmart Aluminum cylinder With a C-10 connection.) Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA