This O-ring is made of black Buna-nitrile (Buna-N) and has a durometer of 70A. It has a square cross-section and can be used across a wide temperature range (-30 degrees F/-34 degrees C to 250 degrees F/121 degrees C). Designed for use in a wide variety of sealing applications, this square O-ring can provide a superior seal to round O-rings in static applications, but is usually not as effective in dynamic applications. This Buna-nitrile O-ring meet standards defined by Aerospace Standard AS568A, which is the Aerospace Size Standard for O-rings. Buna-nitrile can have high tensile strength, and has abrasion, tear, and compression set resistance. It is compatible for use with petroleum, hexafluoroacetone (HFA), hexafluoro-2-butyne (HFB) and hydrofluorocarbon (HFC) fluids, vegetable oil, alcohol, acids, and aliphatic hydrocarbons. Buna-nitrile is vulnerable to acetone, ethers, esters, ozone, sunlight and weathering, and should not be used in ozone-generating electric motors, welding equipment, or in applications with exposure to UV light. The durometer hardness of this Buna 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.