Bushing is a matching part used outside of mechanical parts to achieve sealing, wear protection, etc. It refers to a ring sleeve that acts as a gasket. In the field of valve applications, it is generally used in the valve cover, using corrosion-resistant materials such as polytetrafluoroethylene or graphite for sealing.
The radial runout of the bushing outer cone facing the inner hole (usually called the wall thickness difference) should be high-precision, otherwise the rotating shaft will produce centripetal force due to the fair amount, and it cannot run with bumps, vibration, and music. The wall thickness difference is "0" is the ideal form.