This is the top of the line. The strongest, most durable sealed chain that we offer 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 20% stronger steel the FB has our highest tensile strength rating, 7937 lbs. 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