This metric O-ring is made of black Viton and has a durometer of 75A, a round cross-section, and can be used across a wide temperature range (-15 degrees F/-26 degrees C to 400 degrees F/205 degrees C). Designed for use in a wide variety of sealing applications. Viton (fluorocarbon elastomer) has heat, fuel, and chemical resistance and is compatible for use with non-flammable hydraulic fuels, silicone oil, chlorinated hydrocarbons (trichloroethylene), aromatic hydrocarbons (benzene) and aliphatic hydrocarbons (propane). It works well in high vacuum environments and is vulnerable to low molecular organic acids, ammonia gas, alkalis, amines, glycol-based brake fluids, and super-heated steam. The durometer hardness of this Viton O-ring is 75A. Durometers measure the hardness of a material and its resistance to permanent indentation. A higher durometer value indicates greater resistance to indentation. On a scale of 0 to 100, a value of 0 indicates that a sample was completely penetrated, while a value of 100 shows no indentation in the sample. The letter following the number identifies the shore scale, which is either shore A or D. Shore A is used for rubber while shore D is used for harder plastics. O-rings provide a pressure and fluid seal between cylindrically shaped, overlapping mating surfaces and are commonly seen in engines, faucets, flanges, valves, and various cylinders. They are circular in shape, with a round cross section, and a hole in the center, similar to a doughnut. O-rings are available in a number of sizes, and can be ordered based on required inside diameter (ID), outside diameter (OD), and cross-sectional (CS) diameter.