<Li> In lighting, light bulbs use eighths of an inch for bulb diameter and full inches for fluorescent tube lengths, while the socket is always in millimeters (for example, the standard "medium Edison screw" is E26). On recently introduced Christmas lights, however, millimeters are often used with small globe - shaped bulbs (G30 and G40), and with miniature LED sets, where the standard T13⁄4 (​ ⁄ - inch tube) ones are sometimes called M5 (5 mm miniature; not to be confused with M5 thread). </Li> <P> For properties understood more recently, such as those related to electricity, there is no traditional unit; international units are always used, often in combination with U.S. customary units . One among many examples is in Table 8, chapter 9, of the National Electrical Code Handbook (8th ed .), where resistance of conductors per unit length is given in ohms per thousand feet . </P> <P> Other units are based on customary units, but use power - of - ten factors and metric prefixes . For example, distance to target for a U.S. submarine is expressed in kiloyards rather than some combination of miles, yards, and feet . Telephone transmission line length and loop distances are measured in kilofeet . In some fields of civil engineering (especially structural engineering), and architecture, large loads and forces (such as the weight of a building or the amount of load applied to a column) are measured in kips (kilopounds or 1000 pounds - force) instead of short tons - force (2000 pounds - force), which are used in virtually all other non-metric industries in the United States, as well as in common usage among the public, when dealing with large values of force . </P> <P> The continuing use of U.S. customary units has caused writers to speculate in fiction set in the future about the adoption of the metric system . Many authors have assumed that the United States and the human race in general will use metric units; however, others have assumed the continued use of U.S. customary units or have neglected to take metrication into account . Writers sometimes use customary units simply because American readers and watchers will understand the measurements; other times, they are simply used by accident . The 1966 show Star Trek, for instance, initially used U.S. customary units despite multiple Earth national origins and a setting in the 23rd century . Later, starting with "The Changeling", metric measures were used, albeit inconsistently . Later sequels of the show, such as Star Trek: The Next Generation, and Star Trek: Enterprise (set in the 22nd century), used the metric system exclusively . </P>

When did the us try to adopt the metric system