When they are in a free state prior to installation, EPB plastic sleeve can be found to have excessively large outer diameters and even elliptical outer diameters. First, when in a free condition, an excessively large outer diameter is needed to achieve an interference fit, and can ensure that plastic plain bearings have sufficient snugness when installed in the corresponding mounting hole, which will ensure that the plastic plain bearings do not come loose from their mounting holes during operation. Second, when the outer diameters of plastic plain bearings in a free condition are found to be elliptical, this actually reflects the inherent phenomena of thermal shrinkage following injection molding. As soon as plastic plain bearings are pressed into standard H7 mounting holes, the excellence elastic deformation properties of the plastic sleeve material ensures that the roundness of the sleeves will automatically be corrected at the time of installation, and the inner diameter will comply with the standard tolerance value of E10, F10, or D11. A go-no go gauge should be used to test the tolerance of the inner hole after CSB's interference fit plastic plain bearings are installed in H7 mounting holes.