[6] In 1861, he formed a connection with Fortenbach Brothers (John, Jacob, and Joseph),[7] which resulted in the building at Carlstadt, one of the first establishments in America which manufactured watch cases on an extensive scale; for five years, business was profitable.

When both factories were well under way, Fahys sold his New York store to Ward & Jennings, two of his employees, and gave his undivided attention to his manufacturing interests.

In 1876, he bought the share of the Fortenbach Brothers and moved the Carlstadt plant to Sag Harbor, Long Island.

[8] Fahys' son-in-law,[9] Henry Francis Cook, who was president of the Montauk Steamboat Company, became a partner of Fays & Co. in 1880.

He was a trustee of the Homoeopathic Hospital, the Lafayette Avenue Presbyterian Church,[5] and the Brooklyn Institute of Arts and Sciences.

[5] Fahys and Cook purchased one thousand acres of land in North Haven, a suburb of Sag Harbor, with two miles of frontage on Peconic Bay.