Replacement window kit 133525-G10 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 barium fluoride (BaF2) optical windows enabling spectroscopic analysis across mid-IR wavelengths. Replacement window kit 133525-G10 also includes two replacement 149-0026 Kalrez oring seals intended for instalation on the sample facing side of window, as well as 2 viton orings intended for instalation on the non-sample exposed face of the window.