Unusual types of gramophone records Unusual types of gramophone records 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. The most common diameter sizes for gramophone records are 12-inch, 10-inch, and 7-inch. Early American shellac records were
Gear inches of 27 x 1¼" (ETRTO 630). Strictly speaking, the rolling diameter of a 700c wheel may be significantly higher or lower than 27", depending on the tire size, e.g. nearly 27.5" for a 700x38 tire, or just over 26" for a 700x20 tire. This can be the source of some confusion when comparing gears unless it is clear whether gear inches have been calculated using the actual wheel size or a conventionalised 27". One way to estimate wheel diameter is to add twice the nominal tyre cross-section to the rim diameter. For example, consider a 700c × 23 mm tire,