Standard O-Rings are available in 369 sizes as set up by the Aerospace Standard 568 published by the Society of Automotive Engineers. These sizes are designated by dash numbers shown on the 568 DASH Chart and are standardized by imperial dimensions. Standard O-Rings are specified by their inside diameter and cross section width. AS568 is the most commonly used standard in the U.S. for aerospace, automotive and general industrial applications. For more information, please see: Comparison Properties Chart, PTFE Encapsulated O-rings, Material Shelf Life, and O-ring Groove Design Chart. Buna is also known as: Nitrile, NBR, N, Buna-N.

Nitrile, chemically, is a copolymer of butadiene and acrylonitrile. Acrylonitrile content is varied in commercial products from 18% to 48%. As the nitrile content increases, resistance to petroleum base oils and hydrocarbon fuels increases, but low temperature flexibility decreases.

Due to its excellent resistance to petroleum products, and its ability to be compounded for service over a temperature range of -65 to +275°F(-54 to +135°C), nitrile is the most widely used elastomer in the seal industry today.

Inherently nitrile does not possess good resistance to ozone, sunlight or weather, but this can be substantially improved through compounding.