Nuts & Bolts

Blacksmith skills for Himeji Castle carried on

Himeji City, the land of Kuroda Kanbee, an outstanding 16th-century samurai strategist who never lost a battle in the age of warring provincial lords, boasts Himeji Castle—the first UNESCO-designated World Heritage site in Japan as well as one of Japan’s national treasures—which is a popular destination for tourists and history lovers from overseas and Japan. In addition to this beautiful internationally known castle nicknamed the White Heron Castle, it is worth remembering that the region of Himeji and its adjacent Seiban is a land of a variety of indigenous industries that have been cherished and nursed by history and tradition and that have engaged in day-and-night endeavors to capture the hearts and needs of a fast-changing world. Among these industries is the manufacture of nuts and bolts, whose skills in making have been carried on from those of blacksmiths who produced the nails for Himeji Castle’s wooden fittings. Today, Himeji’s nuts and bolts industry is exploring ways to diversify and upgrade the quality of their products to meet the needs of a high-tech era.

Leonardo da Vinci’s Notebook

Man is said to have invented screw threads by getting the hint from the spiral shells of sea snails or climbing plants using tree trunks for support. Either way, the fact remains that man has been making much use of this invention for many products in various manners. There is no machine that exists today without using screw threads.

Leonardo da Vinci (1452-1519), an Italian polymath of the Italian Renaissance period who left abundant papers covering science and art in his Notebook, had a drawing of the fundamental principle of screw thread processing using taps and dies. He also left in his Notebook a drawing of a screw-cutting lathe having a modern structure that has two lead screws, replacement gears, etc.

From other various historical documents including one by Georgius Agricola (1494-1555), a German scientist, it is now believed that metal bolts, nuts, marine screws, wooden screws, and the like were invented around the year 1500. In those days, screw threads were used to build carriages, carts, and so on. Some chest armor of soldiers was equipped with breast plates that were fastened with screw threads. Louis XI, the King of France (1461-1483), is said to be a user of a wooden bed that was set up using metal screw threads.

First Japanese to witness fastening screws

In 1543, a storm forced a Chinese junk to anchor at Tanegashima, an island off the southern tip of Kyushu. Aboard it were Portuguese who had matchlock muskets that no resident had ever seen. Tanegashima Tokitaka, the samurai lord of the island, paid a huge sum and purchased two matchlock muskets from them and handed one of the two to Yaita Kinbei a swordsmith, ordering him to produce a copy of the musket and study the mechanism of firing. After about one year of hard work, the swordsmith managed to produce one. Kinbei is said to be the first Japanese who witnessed European screws. The buttstock of the musket was closed with a breechblock screwed into the stock.

For Kinbei, the swordsmith, the manufacture of the buttstock’s external screw seemed rather easy. It seems that he cut out the shape with file, following a string wound like a coil. Yet the manufacture of the breechblock must have been tough work—drilling the barrel helically so that the breechblock’s internal screw could be tightly inserted.

In those days, swordsmiths could rely upon only files and chisels as metalworking tools. Kinbei is believed to have employed the hot forging method. The matchlock musket resulting from his hard work, Japan’s first home-made gun, is today on exhibition at the Tanegashima Development Center (Gun Museum) in the island’s Nishinoomote City, Kagoshima Prefecture, together with the original matchlock musket that he took apart.

ISO screw threads fasten the world

In the 1770s, as the Industrial Revolution advanced in England, demand for nuts and bolts increased explosively. Though these fastening materials were produced by specialty manufacturers, each machine maker placed his orders for his own products with personalized diameters and pitches. It was no surprise that merits of mass production could not be realized due to demand for so many kinds of screw threads.
Sir Joseph Whitworth (1803-1887), a British engineer who engaged in the improvement of screw cutting lathes developed by machine tool inventor Henry Maudslay (1771-1831), conducted a widespread survey on those nuts and bolts characterized by un-unified shapes and sizes. At last, in 1841, he made public the screw thread called the Whitworth thread and worked hard to promulgate it. As a result, it grew into the British Standard Whitworth system and was later officially adopted as the British Standards (BS).

Other countries followed the path of standardization. The United States adopted the American Standards and France, the Système International d’Unités (SI). While other European nations adopted the metric screw threads of the International Society of Automation (ISA), the three countries of the United States, Great Britain, and Canada agreed to adopt the Unified Thread Standards (UTS) for their military hardware.

As these standards were adopted individually, the International Organization for Standardization (ISO) was established in 1947 as an independent, non-governmental membership organization. In 1957, the world’s largest developer of voluntary international standards adopted the ISO metric screw thread, similar to the ISA metric screw thread, as well as the ISO inch standards for the UTS.

In Japan, the Japanese Industrial Standards (JIS) stipulates the use of the ISO metric screw threads for general purposes. For airplanes and other necessary purposes, the adoption of the ISO inch standards is required.

History in Himeji

The Shirahama area of Himeji City faces the Inland Sea. People there were engaged, from around the 16th century, in agriculture, smithery, salt farming, and so on. Blacksmiths made various kinds of bended nails to be used for wooden fittings for Himeji Castle as well as marine screws. In the modern Meiji era, they faced declining demand for Japan’s traditional nails, but with their skills using bellows and other tools for smithery, they found a way out in manufacturing nails for ships, anchors, chains, rivets, nuts, etc.

The first type of nuts they produced were hand-forged round-head nuts, utilizing punch scraps from shipbuilding. Hand-cranked taps were used for drilling. Nut production was accelerated after Sueharu Segawa started to produce nuts for shipbuilding around the early 1900s. In 1917, after the end of World War I, Seitaro Yano, Yosamatsu Hamaguchi, and Toji Matsui launched their respective factories to produce nuts and bolts for ships and trains. Two years later, a certain Amishima established an ironworks dedicated to flat iron nuts. In 1923, Tomiichi Okazaki who had been working for a chain factory inaugurated a specialty nut factory.

After the production of flat steel nuts started, the number of factories increased and the nut production volume jumped in Himeji. When machines to manufacture nuts from round steel were introduced into Himeji from Osaka in 1935, the local, traditional nut manufacturing methods were eradicated and the new system became the predominant one. Shirahama nuts from round steel occupied a major part of Japan’s total output of large-diameter nuts until the 1960s, when the hot forging system took over.

Demand has been stagnant for Himeji’s nuts and bolts in recent years since many machine manufacturers left Japan for overseas. Also, business continues to be sluggish in the construction and other domestic industries. At the same time, however, new demand is on the rise for high-grade precision products to be used for mechatronics and robots amid the fast advancement of the mechanical industry. The nuts and bolts industry of Himeji is ready to address the present challenge to put diversified, high-end products onto the market and seek ways to coexist with cheap imported products.