As part of their continuing quality improvement program, the RK Chain Factory has made a running production upgrade to their best selling XSO chain line. The XSO chains features RK's proprietary "RX-Ring" seal design and is offered in 428, 520, 525 & 530. All versions are available in a variety of colors. Viewed in cross-section, the RK "RX-Ring" has two contact lips and one lubrication pool 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.