British Standard O-Rings are very similar to Standard O-Rings in the fact that they are both standardized imperically. The British Standard however, incorporates some extended sizes in the 1/4" nominal cross section group for an even broader application range. British Standard O-Rings serve a variety of industries including aerospace, paint, food, and chemical transport. PTFE is also known as TFE and Polytetrafluoroethylene. For more information, please see: Comparison Properties Chart, PTFE Encapsulated O-rings, Material Shelf Life, and O-ring Groove Design Chart.