In the moving parts, the parts are worn due to long-term friction, and the parts must be replaced when the gap between the shaft and the hole is worn to a certain extent. Therefore, the designer chooses the material with lower hardness and better wear resistance as the shaft sleeve or bushing in the design, which can reduce the wear of the shaft and the seat. When the shaft sleeve or bushing is worn to a certain extent, it can be replaced, which can save the cost of replacing the shaft or seat. In general, the bushing and the seat use an interference fit, and the shaft uses a clearance fit. Because no matter what, it is unavoidable to avoid wear and tear, and can only prolong the life, and shaft parts are relatively easy to process.

There are also some new designers who don't like this design, thinking that it will increase the cost of manufacturing. However, after a period of use, it is still necessary to transform in this way during maintenance, which will easily reduce the accuracy of the equipment. The reason is very simple, the secondary processing is not enough to ensure the position of the center of the seat hole, and the shaft sleeve is at a lower speed at some speeds. Places with high radial loads and high clearance requirements (such as camshafts) are used to replace rolling bearings (in fact, the bushing is also a sliding bearing). The material requires low hardness and wear resistance, and the inner hole of the shaft sleeve is ground and scraped to achieve high matching accuracy. There must be an oil groove for lubricating oil on the inner wall, and the lubrication of the shaft sleeve is very important.