The overwhelming majority of records manufactured have been of certain sizes (7, 10, or 12 inches), playback speeds (33, 45, or 78 RPM), and appearance (round black discs). However, since the commercial adoption of the gramophone record (called a phonograph record in the U.S., where both cylinder records and disc records were invented), a wide variety of records have also been produced that do not fall into these categories, and they have served a variety of purposes. Unusual sizes The most common diameter sizes for gramophone records are 12-inch, 10-inch, and 7-inch. Early American shellac records were all 7-inch until 1901, when 10-inch records were introduced. 12-inch records joined them in 1903. By 1910, other sizes were retired and nearly all discs were either 10-inch or 12-inch, although both sizes were normally a bit smaller than their official diameter. In Europe, early 10-inch and 12-inch shellac records were produced in the first three decades of the twentieth century. 7-inch children's records were sold before World War II but nearly all were made of fragile shellac, not an ideal material for use by children. In the late 1940s, small plastic records, including some small picture discs, replaced them. Ten-inch children's records were made as well, but the 7-inch size was more compatible with small hands. The 7-inch size was also used for flexi discs which were popular in Japan where they were known as sound-sheets and were often in traditional round format. In other areas, flexi discs were usually square and often included in a magazine (see Unusual materials and uses below). Numerous unusual diameters have been produced since the early 1900s ranging from 2 to 19.7 inches. Oddly shaped discs were also produced (see Unusually shaped discs below). Unusual speeds The most common rotational speeds for gramophone records are revolutions per minute (rpm), 45 rpm, and 78 rpm. Established as the only common rotational speed prior to the 1940s, the 78 became increasingly less common throughout the 1950s and into more modern decades as the 33 and the 45 became established as the new standards for albums and singles respectively. Throughout the history of the recording industry, however, numerous unusual turn-speeds ranging from 3 to 130 rpm have been utilized for a variety of purposes. Varying and variable play-speeds In the early 1920s, the World Record Company in the U.K. introduced longer-playing records with speeds measured in inches per second