520 FB O-Ring Chain Moose Racing This is the top of the linethe strongest, most durable sealed chain Moose Racing offers FB = Fine Blanking, an incredibly precise manufacturing process that yields perfectly cut links. Tight tolerances make the plate, pin, and bushing union accurate and strong Due to the accuracy of the cuts and the use of stronger alloyed steel the FB has our highest tensile strength rating, nearly 8,000 lb. Special sealing rings are chemically treated to gain strength and reduce friction. The FB treatment allows the O-rings to be impregnated with grease. FB rings are stronger and more durable than X-rings, with significantly less friction Gold links and rollers, silver inner plates, pins and bushings Clip-type connecting link included Replacement connecting link available