Replacement window kit 133525-G13 is a routine maintenance kit designed for use with MultiGas 203X/603x Fourier Transform Infrared (FTIR) gas analyzers having 180 or 200mL gas cell volumes with a pathlength of 5m, 10m, or 35cm. This kit includes two Zinc Selenide (ZnSe) optical windows enabling broad spectroscopic analysis across mid-IR wavelengths while supporting a wide variety of sample types due to the materials low reactivity. Replacement window kit 133525-G13 also includes four replacement 149-0026 Kalrez oring seals. (If converting from an alternate window material alternative ZnSe Upgrade Kit 1042485-002 should be ordered.)