The design, development, and production of caster swivel wheels often encounter challenges related to different measurement units, such as metric, American, and imperial units. These units are widely used across the world, including in systems like the atomic unit system, Taiwan system, international unit system, Planck unit system, natural unit system, imperial unit, and the municipal unit system used in China. It is essential to address these diverse measurement units when working on caster swivel wheel projects.
Let's start by discussing International Units, which are also referred to as metric or metric units. Most of us are familiar with it, but I will give a brief explanation. The metric system, formerly known as the Universal Metric System, is the most widely used standard unit system globally. The International System of Units was developed in the late 18th century by scientists and was first adopted by France during the French Revolution in 1799. The standard unit of length was based on the earth's meridian and was defined as 1/40 millionth of the length of the meridian passing through Paris; this unit was named 'meter' or 'metre.' Similarly, the standard unit of capacity was based on one thousandth of a cubic meter and was named 'liter.' The kilogram was defined as the mass of one liter of pure water at 4°C. In 1875, the International Bureau of Weights and Measures was established in Paris by 17 European and American countries. The bureau was responsible for producing and preserving platinum-iridium alloy prototypes for use as international standards for length and mass.
The SI system has become the go-to measurement system worldwide as a result of its simplicity and convenience. With the exception of the United States, Myanmar, and Liberia, which do not primarily employ the SI system, all other countries use it as their primary weights and measures system. Even former imperial countries such as Canada, the UK, and Australia have converted to the SI system in the latter half of the 20th century. However, it is worth mentioning that in the field of aviation control, the imperial system is still in use internationally, with factors such as flight altitude measured in feet.
In 1928, the government of the Republic of China promulgated the Weights and Measures Law, stipulating that the "Universal Metric System" should be adopted as the standard system, and the "Municipal System" was temporarily set up as a transitional system, that is, 1 meter is 3 city feet, and 1 liter is 1 city liter. 1 kilogram is 2 kilograms. The reformed municipal system was adapted to the habits of the people, and it was easy to convert from the metric system, and gradually accepted by the public. After 1949, the municipal system became popular throughout the country. In 1984, the State Council issued an order to adopt the legal measurement units of the People's Republic of China (abbreviated as legal units) based on the International System of Units and some non-SI units. Since January 1, 1991, the legal unit has become the only legal measurement unit in China.
The use of inches to describe caster specifications is primarily rooted in the historical development of casters. While China has been knowledgeable about designing and utilizing caster wheels for a significant period, the term "casters & wheels" as well as their mass production and sales originated from reforms and developments. In those times, China predominantly functioned as an OEM manufacturer with the United States and other countries using imperial units being the major recipients of batch exports. As a result, the specifications of casters were customized according to customer requirements, leading to their frequent use of inches as the unit of measurement. Consequently, this practice became the norm.