SAN FRANCISCO — Chris Maling says he approached Finnegan, Henderson, Farabow, Garrett & Dunner with a straightforward request: obtain a patent on his idea for a screwless eyeglass hinge.

Finnegan says it did exactly what Maling wanted: It obtained four patents on his invention.

The two are nevertheless facing off over a claim of legal malpractice. By the time the patents were granted, Maling alleges, they were useless because a much larger competitor had come up with its own version. And the firm that represented the competitor at the U.S. Patent and Trademark Office: Finnegan.