Metric O-Rings are employed in specialized applications and, like the name suggests, are standardized by metric dimensions. With a wide variety of sizes available, Metric O-Rings fill in the gaps left by the standardized AS568 o-ring chart. Metric O-Ring sizing is determined by the o-ring's inside diameter and cross section width. 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. For more information, please see: Comparison Properties Chart, PTFE Encapsulated O-rings, Material Shelf Life, and O-ring Groove Design Chart.