bushing
A type of plain bearing, a cylindrical lining designed to reduce friction and wear inside a hole, often used as a casing for a shaft, pin or hinge.
bushing: the hard-wearing liner that lets shafts spin freely
A bushing is a cylindrical sleeve pressed or threaded into a hole to serve as a bearing surface. Where a shaft, pin, or bolt passes through, the bushing takes the wear instead of the parent material, protecting it from friction and abrasion. The bushing itself is typically softer or more slip-friendly than steel, allowing smooth rotation with minimal force.
Bushings come in two main forms: solid bushings, which are simple cylinders of bronze, rubber, or polymer pressed into place; and flanged bushings, which have a shoulder or collar to locate them and stop them from disappearing into the hole. Bronze bushings dominate in machinery where oil lubrication is standard. Rubber or elastomer bushings are common in automotive and vibration-damping applications, where they also isolate noise and deflection.
Materials and failure modes
Self-lubricating bushings made from bronze-tin or bronze-lead alloys can run dry or with light grease, reducing maintenance. Polymer bushings (often acetal or nylon) need no lubrication but have lower load limits and higher creep under sustained pressure. Bushings fail through scoring (spalling of the inner surface), which happens when lubrication fails, particles embed in the surface, or radial loads exceed design limits. Once scored, a bushing must be replaced; the damage does not repair itself.
Installation requires care: bushings are driven home with a press or careful hammer work, and they must be parallel to the hole to avoid binding. Some designs have a small axial clearance or groove to trap lubricant. Undersized holes cause installation damage; oversized holes lead to bushing tilt and rapid wear. Proper design calls for the bushing length to exceed the loaded zone by a margin of at least the bushing diameter.
Bushings sit between simple bearings and precision rolling-element bearings in the cost and performance spectrum. They suit low-speed, high-load, or intermittent-duty applications where the cost and bulk of a ball bearing is unjustified. They are also used inside gearboxes, hinges, and linkages where a full rolling bearing cannot fit or tolerate the shock loads that machinery generates.