Hargis Industries, Inc. (Hargis) (defendant), manufactured fasteners for use in the construction industry under the trade name “SEALTITE.” B&B Hardware, Inc. (B&B) (plaintiff) manufactured fasteners for use in the aerospace industry under the trade name “SEALTIGHT.” Hargis sought to register its trade name pursuant to the Lanham Act, 15 U.S.C. § 1051, through a United States Patent and Trademark Office (PTO) administrative process. B&B opposed the registration in a proceeding before the Trademark Trial and Appeal Board (TTAB). Thereafter, B&B filed suit in federal district court against Hargis for trademark infringement. While the action was pending in district court, the TTAB held for B&B, concluding that Hargis’s mark could not be registered because it too closely resembled B&B’s mark and could cause confusion. B&B argued in district court that Hargis could not contest the likelihood of confusion due to the preclusive effect of the TTAB’s decision. The district court disagreed, reasoning that the TTAB was not an Article III court. After a trial, a jury held for Hargis. B&B appealed. The court of appeals affirmed because (1) the TTAB used different factors to evaluate likelihood of confusion, (2) the TTAB placed too much emphasis on the appearances and sounds of the two marks, and (3) Hargis had the burden of persuasion before the TTAB while B&B had the burden of persuasion before the district court. The United States Supreme Court granted certiorari to review.