As part of their continuing quality improvement program, the RK Chain Factory has made a running production upgrade to their best selling 520XSO chain. The new upgraded 520XSO chains feature heat treated hi-carbon alloy steel components with seamless rollers and shouldered bushings, and are fitted with RK's proprietary RX-Ring seal design. RK's new 520XSO chains offer quality, performance and unbeatable value, for all but the most demanding high performance application. RK's RX-ring chains feature an X-ring shaped seal. Viewed in cross-section, the X-ring has two lubrication pools and seal points versus the single seal point/pool design of a regular o-ring chain. RX-ring technology offers less torsional friction, increased high-stress performance, and a 30% longer wear life compared to standard o-ring chains. RK's new RX-ring chains offer tremendous value, plus true quality and performance for all but the most demanding high performance applications. Pin Length in mm: 19.9mm. Maximum Wear Life Index: 750. Maximum Tensile in lbs/Ft: 8500lbs/ft. Masterlink Type: Rivet. Weight in Lbs per 100 Links: 3.36lbs. Max cc: 750cc Street / 750cc Off-Road. 19.2 Links per foot. 15.875mm Pin to Pin center. Your original purchase of RK sealed-ring chain is warranted to be free of defects in material and workmanship for 20,000 miles of street riding or one-year of off-road use. There is absolutely no warranty of any kind for an RK Chain used in ANY racing competition.