XRU (inner and outer ring as a whole, with mounting holes), because of the mounting holes, do not need to fix flange and support seat during installation. In addition, since both the outer and inner rings are integral, the installation has little impact on performance, thus achieving stable rotation accuracy and torque. Suitable for outer and inner ring rotation. Because XRSU structure is the same as XRU, the thinner design, so compared with XRU has a more compact size shape and higher rotation accuracy, suitable for the installation space is limited and requires higher precision occasions. The XV series has mounting holes on the outer ring, but not on the inner ring.