The XSO chains features RK's proprietary "RX-Ring" seal design and is offered in 520, 525 & 530. All versions are available in a variety of colors. Viewed in cross-section, the RK "RX-Ring" has two lubrication pools and seal points versus the single seal point/pool design of a regular o-ring chain. RK's XSO chains offer quality, performance and unbeatable value, for all but the most demanding high performance application.