WD-40 (Benedek Alpar/shutterstock.com)

There's a club in San Diego more exclusive than the Soho House and harder to get into than Harvard. It requires a special key, confidentiality agreements, passage through a bank vault, and typically an executive position. The only privilege is knowing the secrets of the world's most famous lubricant, reports the Wall Street Journal.

"Entering there was like entering Fort Knox, frankly," said Steve Brass, CEO of WD-40, who was admitted about 18 months ago — more than three decades after he joined the company. The handwritten formula is stored in a vault at Bank of America, at an undisclosed location in San Diego. In the last 30 years, it has left the vault only three times.

One of those was when former executive Garry Ridge rode into Times Square on horseback, wearing armor and carrying the formula to celebrate the company's 50th anniversary on the Nasdaq. In 2018, an armored vehicle transported Ridge, handcuffed to a metal briefcase containing the formula, from one vault to another.

The notebook contains the 40th attempt at the formula — and the 39 previous failures. (WD stands for Water Displacement.) Most WD-40 employees have never seen it and never will, including the head of research and development. They use a coded version to preserve the secret. The company never filed for a patent because patents eventually expire and become public. As a trade secret, the formula is protected indefinitely.