MONODZUKURI

No Screws Loose at Hard Lock

Securely fastened screws are essential for the safety of all manner of applications vital to modern society. The Hard Lock Nut, an innovative product released by Hard Lock Industry Co. in 1974, prevents screws from loosening, which explains why it is now being adopted around the world. Miho Yanagisawa reports.

After graduating from university, Katsuhiko Wakabayashi, the founder and president of Hard Lock Industry Co., worked as a design engineer with a valve manufacturer. One day in 1961, an idea occurred to Wakabayashi when he saw a nut fitted with a device that prevented unscrewing at an international fair. The nut used a stainless steel wire for holding it in position and preventing it from unscrewing. Wakabayashi’s idea was to replace the wire with a leaf spring. Through this improvement, Wakabayashi developed the U-Nut, a nut that didn’t loosen.

Wakabayashi left his employer and started his own business. He offered samples of U-Nut to many manufacturers, and the product became well known since it hardly loosened at all. Its sales continued to grow steadily.


However, as their sales grew and the product came to be used in a wider variety of applications, complaints that the nuts loosened started to be heard. These complaints often involved heavy equipment that is exposed to continuous heavy impacts over a long period of time, such as those used in rock excavation and pile driving.

Wakabayashi concentrated his thoughts on resolving this issue, and one day a light went on inside his head while he was looking at a torii gate at a Shinto shrine. Wedges for reinforcement are hammered in over the wooden beam that connects the two columns of the gate.

“This principle can be applied,” he thought.

That was in 1973, one year before the birth of Hard Lock Nut.

A wedge hammered between the nut and bolt could function as a stopper, but Wakabayashi couldn’t ask his customers to hammer in a wedge. It was necessary to create a nut with a built-in wedge.

After repeated trial and error, Wakabayashi decided to combine concave and convex nuts. The inner side of both nuts is slanted, and after fitting on and tightening the upper concave nut over the lower convex nut, it works just like a hammered-in wedge. Hard Lock Nut, the nut that never becomes loose, was born.

“We will never get complaints again.” At that moment Wakabayashi felt both relieved and happy.


Two years after the birth of Hard Lock Nut, the company got a large order from Hanshin Electric Railway Co., one of the major private railways connecting Osaka and Kobe. Hanshin Electric Railway had a problem with bolts that loosened easily at points where curved rails come together, necessitating daily inspection by safety personnel. By adopting Hard Lock Nut, the railway company was able to save labor and cost while maintaining safety. This success opened the door for Hard Lock Industry to expand its sales channels to expressways, bridges, iron towers, high-rises, industrial machinery and other areas. In 2003, Hard Lock Nut was adopted in Taiwan for connecting bullet train rails, and at railway switches in the United Kingdom and Australia.

For the thirty-six years since its birth, Hard Lock Nuts have never caused an accident due to their loosening. “Monodzukuri [creative manufacturing], above all, is about making users happy.”

Wakabayashi believes so, and is still working hard to develop even higher quality and better functioning products.

Company name:	Hard Lock Industry Co., Ltd.
President:	Katsuhiko Wakabayashi
Head office address:	1-6-24, Kawamata, Higashi-Osaka-City, Osaka, 577-0063
Business:	Manufacture and sale of nuts, screws and pins
Website:	http://www.hardlock.co.jp/en/index.php

Miho Yanagisawa is a freelance writer.