Plain bearings and sleeve bearings (also referred to as bushings or journal bearings) are used to constrain, guide or reduce friction in rotary or linear applications. They function via a sliding action instead of the rolling action used by ball, roller, and needle bearings. Plain bearings and sleeve bearings are made from a variety of materials and are often self-lubricating to provide smooth operation and greater durability. Hydrostatic, hydrodynamic, and fluid film bearings are plain bearings and sleeve bearings that rely on a film of oil or air to create a clearance between the moving and stationary elements. Some products are designed for extreme environments and can withstand high or low temperatures. Others are suitable for hazardous environments with high levels of shock and vibration. Applications for plain bearings and sleeve bearings include food processing machinery, home appliances, packaging equipment, office machines, and automotive equipment.

There are several important dimensional specifications for plain bearings and sleeve bearings. Examples include shaft outer diameter (OD), bearing inner diameter (ID), bearing OD, length, flange diameter, flange thickness, and housing bore. Both metric and English or imperial pitch bearings are available. Typically, manufacturers use a standard numbering system for bearings with metric diameter bores. For bore sizes 04 and up, multiplying the size by 5 yields the bore in millimeters. Hexagonal bores are measured across the flats. Tapered bores are measured by the smaller diameter. In terms of bushing styles, products with cylindrical or flanged bushings are commonly available.

Plain bearings and sleeve bearings (also referred to as bushings or journal bearings) are used to constrain, guide or reduce friction in rotary or linear applications. They function via a sliding action instead of the rolling action used by ball, roller, and needle bearings. Plain bearings and sleeve bearings are made from a variety of materials and are often self-lubricating to provide smooth operation and greater durability. Hydrostatic, hydrodynamic, and fluid film bearings are plain bearings and sleeve bearings that rely on a film of oil or air to create a clearance between the moving and stationary elements. Some products are designed for extreme environments and can withstand high or low temperatures. Others are suitable for hazardous environments with high levels of shock and vibration. Applications for plain bearings and sleeve bearings include food processing machinery, home appliances, packaging equipment, office machines, and automotive equipment.

There are several important dimensional specifications for plain bearings and sleeve bearings. Examples include shaft outer diameter (OD), bearing inner diameter (ID), bearing OD, length, flange diameter, flange thickness, and housing bore. Both metric and English or imperial pitch bearings are available. Typically, manufacturers use a standard numbering system for bearings with metric diameter bores. For bore sizes 04 and up, multiplying the size by 5 yields the bore in millimeters. Hexagonal bores are measured across the flats. Tapered bores are measured by the smaller diameter. In terms of bushing styles, products with cylindrical or flanged bushings are commonly available.

Plain bearings and sleeve bearings use several surface materials. Sintered bronze is porous and can be impregnated with oil, graphite, or polytetrafluorethylene (PTFE). Sintered bronze is not suitable for heavy loads, but is often used in applications where lubrication is difficult or inconvenient. PTFE, a heat-tolerant polymer, is a fluorinated thermoplastic with outstanding chemical resistance, low leachability, and excellent lubricity. Teflon^®, a registered trademark of DuPont Dow Elastomers, is a proprietary form of PTFE used with many plain bearings and sleeve bearings. Nylon, a category that comprises several grades of polyamides, is another commonly used 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. Some plain bearings and sleeve bearings are surfaced with oil-impregnated hardwood, usually in agricultural applications. Others contain self-lubricating surfaces made of molten graphite and metal.