Ball and roller take-up bearings are usually made from a carbon or stainless steel. Plain bearing take-ups are made from bronze or plastics such as polytetrafluoroethylene (PTFE), nylon, and Acetal polymers. Polytetrafluoroethylene (PTFE), a heat-tolerant polymer, is a fluorinated thermoplastic with outstanding chemical resistance, low leachability, and excellent lubricity. Nylon, a category that comprises several grades of polyamides, is commonly used as a bearing surface material because of its toughness, resistance, and pressure ratings. Semi-crystalline Acetal polymers offer excellent lubricity, fatigue resistance, and chemical resistance; however, they suffer from outgassing problems at elevated temperatures and become brittle at low temperatures.Bearing housings are usually manufactured from cast iron or steel, while take-up frames are typically made of steel or cast iron.Ball bearings use balls between the inner and outer races to reduce friction.