Round, Translucent, 030 Polyurethane O-Rings, 70A Durometer, 1-5/8" Id, 1-3/4" This O-ring is made of translucent polyurethane and has a durometer of 70A. It has a round cross-section and can be used across a wide temperature range (-60 degrees F/-51 degrees C to 212 degrees F/100 degrees C). Designed for use in a wide variety of sealing applications, this polyurethane O-ring meets standards defined by Aerospace Standard AS568A, which is the Aerospace Size Standard for O-rings. Polyurethane is resistant to oil, weather, ozone , heat, electricity, abrasion, tearing and many chemicals. It performs well in low temperatures, but is not recommended for continuous use in high temperatures or with super-heated steam. The durometer hardness of this polyurethane O-ring is 70A. 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 softer plastics, 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 various AS568A dash sizes, which is the standardized sizing for O-rings, and defines the nominal inside diameter (ID), outer diameter (OD), and cross-sectional (CS) diameter of an O-ring. Urethane O-Rings are compatible with hydraulic fluids, weak acids and bases, and mixtures containing less than 80 percent aromatic constituents