Hard Lock Industry: Supplying Self-Locking Nuts to the World

As many as 20,000 pairs of nuts and bolts are required to assemble the 16 cars on a Shinkansen bullet train. With the trains whizzing along at 250 kilometers per hour, a single loose bolt could cause a major disaster. Painstaking safety checks and regular retightening of nuts is one way to prevent accidents, but one that involves serious investments of time and money. One of the unsung heroes whose work has enabled the Shinkansen to operate safely and affordably year after year is Wakabayashi Katsuhiko, the 78-year-old president of Hard Lock Industry Co., Ltd, who revolutionized rail safety by inventing a unique nut that never comes loose.

Corporate Data
Company name: Hard Lock Industry Co., Ltd.
Address: 1-6-24 Kawamata, Higashi Osaka City, Osaka 577-0063
Representative: Wakabayashi Katsuhiko, President
Business: Manufacture and sales of Hard Lock Nuts, Hard Lock Bearing Nuts, Space Lock Nuts, Hard Lock Set Screws, and other products (all patented)
Capitalization: ¥10 million
Employees: 49
Website: http://www.hardlock.co.jp/en

Applying the Wedge Principle with Two Nuts

The idea behind the Hard Lock Nut is simple: it uses the wedge principle to lock the nut into place. Hammering a wedge between the nut and bolt is enough to prevent loosening. But this is not realistic in the real world, since it would require workers to drive in a wedge every time they screwed a nut and bolt together.

Wakabayashi racked his brains for a way to create a similar wedge-like effect using nuts alone. The solution he came up with was to use two differently shaped nuts for each bolt: one concave, the other convex. The concave nut (the upper nut) has a perfectly spherical concavity, but the convex nut (the lower nut) has a small eccentricity, with a thin wedge on one side and a thick wedge on the other. When the concave nut is tightened over the convex nut, the effect produced is the same as driving in a wedge with a hammer.

A Life-Changing Encounter

Hard Lock President Wakabayashi Katsuhiko

Wakabayashi’s thoughts first turned to the possibilities of nut design after a visit to an international trade fair in Osaka in 1961, where he came across a nut with a mechanism for preventing the bolt from loosening. When he took a sample home for inspection, he found that the bolt featured a complicated mechanism using stainless-steel wire to keep the nut firmly attached to the bolt. This made it expensive. Surely, Wakabayashi thought, there must be a simpler, less-expensive way of locking nuts into place.

What he first came up with was a method of attaching a leaf spring to the threads of a bolt. This proved quite effective at preventing nuts from loosening, and in 1962 Wakabayashi along with his brother and a friend established a company to produce and sell the new kind of nut, which he named the “U Nut.” For the next decade, the business enjoyed steady growth. But Wakabayashi eventually found himself up against a new difficulty.

Cases started to emerge in which Wakabayashi’s U Nuts were coming loose, particularly when they were used in excavators, pile drivers, and other equipment subjected to continuous strong jolts. And the complaints only became more frequent as the range of industries and applications using the nut grew. Wakabayashi realized that he would have to go back to the drawing board.

The Torii Gateway to Shrines

One day late in 1973, inspiration struck. He was looking up at the torii marking the entrance to Sumiyoshi Shrine not far from his home in Osaka, when his eye was caught by the wedges holding the tie-beam in place. “If I could use a wedge like that,” he said to himself, “surely the nuts would be strong enough to withstand any vibrations.” Immediately he returned to the basic question of how to drive a wedge into the space between nuts and bolts. This hint from one of the shrines that are everyday objects in Japan “may have been a kind of divine inspiration,” he says.

The Beginnings of Hard Lock Industry

Convinced that he was on to a winner, Wakabayashi decided to stake everything on his idea and founded the present company in 1974. He sold the U Nut business to associates for next to nothing. Still produced, the U Nut continues to be one of Hard Lock’s major competitors today.

A major breakthrough for the new product came in 1976 when Wakabayashi won a contract with an Osaka-based railway company to supply the nuts for its electrical machinery. From there, the business went from strength to strength. The nut achieved excellent results in a vibration test conducted under the stringent National Aerospace Standards of the United States, said to be the most exacting in the world. Although it costs four or five times more than conventional nuts, the nut requires no further maintenance once it is installed. This results in significant savings and works out much more economical in the long run.

The company’s products are used in a wide range of fields worldwide, including machine tools, shipbuilding, and the automotive industry.

Hard Lock Nuts are used by railways in Australia, Britain, China, Poland, and South Korea, and they have helped Taiwan High Speed Rail achieve a record of no serious accidents since it went into service in 2007. When the company's outstanding safety record was featured in a BBC documentary about rail accidents in 2006, Britain's railway companies switched to the Hard Lock Nut almost overnight.

Hard Lock nuts are not limited to the world’s railways. The nuts have also been used in the Akashi-Kaikyō Bridge, the longest suspension bridge in the world, and the Tokyo Sky Tree, the world’s tallest free-standing broadcasting tower. Today the nuts are used around the world in heavy equipment such as marine excavators. The nuts have even been used in the Space Shuttle launch pads.

The company has also been approached by the likes of Boeing and Rolls-Royce Holdings. Wakabayashi and his team are currently engaged in research to develop lighter nuts for use in aircraft.

The Ardor of the Inventor

Visitors take delight in Wakabayashi’s model railroad collection, which includes a miniature train they can ride.

Even after the international success of the Hard Lock Nut, Wakabayashi refused to rest on his laurels. He has gone on to develop many more innovations since then, including the Space Lock Nut (a single nut with enhanced efficiency) and the Hard Lock Bearing Nut (a locknut for use in roller bearings).

Wakabayashi is also a serious collector of model trains, which he credits with inspiring some of his most innovative ideas. An impressive collection of model trains is on display on the second floor of one of the company’s factories. One highlight is a miniature train large enough to carry 10 people round a 100-meter track. Visitors to the factory clamber eagerly on board. “At work and at play,” he says, “nothing gives me more pleasure than making people happy.” Needless to say, the rails on the track are fastened with the Hard Lock Nut, so the safety of the passengers is assured.

(Originally written in Japanese. Photographs by Onoe Tatsuya.)