Retainers are the core component of the bearings necessary for machines and transportation vehicles. Bearings made with special copper alloy are more compatible with steel bearings than bearings made with iron plate, the material most other bearings are made from. In addition, copper alloy exhibits outstanding durability under severe conditions. For this reason, copper alloy retainers are imperative for transportation vehicles, such as aircraft, shinkansen and other railway vehicles requiring safety, comfort and durability as they carry precious lives, as well as for precision instruments and machine tools.