Raising the hurdle for proving secondary considerations, the US Court of Appeals for the Federal Circuit found that the “coextensiveness” requirement for purposes of nexus requires that the practicing product be “essentially the claimed invention.” FOX Factory, Inc. v. SRAM, LLC, Case No. 18-2024, -2025 (Fed. Cir. Dec. 18, 2019) (Prost, J.).

Bicycle chainrings are the toothed disks to which bicycle chains engage. SRAM owns a patent directed to an improved chainring structure that better maintains the chain, obviating the need for extraneous structures. The independent claims of the patent recite a chainring with alternating narrow and wide tooth tips and teeth offset from the center of the chainring. Some of the claims recite tooth tips offset toward the body of the bicycle (inboard offsets) and other claims recite teeth offset away from the body of the bicycle (outboard offsets). The specification discloses additional chainring features that are not recited in the claims. Each of the disclosed but unclaimed features contribute to improving chain retention. For example, the specification discloses forwardly protruding tip portions that function to engage a chain link earlier than a chain lacking the tip portion, a hook feature formed on the rear flank of each tooth to provide better guiding of the chain, and also that the narrow and wide teeth preferably fill at least 80% of the axial distance of the corresponding space in the chain link (>80% gap filling). SRAM sells 13 different versions of its “X-Sync” chainrings, 12 of which embody the inboard offset claims and one of which embodies the outboard offset claims. The X-Sync chains also embody the unclaimed features disclosed in the specification.

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