Reflector behind the glass helps see oil levels, presence of liquids, color, quality of a fluid. 304 Stainless Steel Gasketed Glass Sight for visual observation of liquid levels and their condition. These sight glasses are typically used in any application where oil or fluid inspection is essential. The housing is a 304 Stainless Steel fitting with U.S. standard NPT threads conforming to ASME B1.20.1. Use traditional installation tools and Teflon tape or pipe sealant. These sight glasses have a Buna-N internal seal for good chemical compatibility with Petroleum oils and fluids; Cold Water; Silicone greases and oils; Dibasic Acid Ester (Diester) based lubricants (MIL-L-7808); Ethylene glycol base fluids (Hydrolubes). Not Recommended for: Halogenated hydrocarbons (carbon tetrachloride, trichloroethylene); Nitro hydrocarbons (nitrobenzene, aniline); Phosphate ester hydraulic fluids (Skydrol, Fyrquel, Pydraul); Ketones (MEK, acetone); Strong Acids Ozone; Automotive brake fluid.