Rotary Dial - General Form

General Form

The dial, also called the finger wheel, is circular. Ten finger holes perforate it in a partial ring near the perimeter. The dial is mounted via a shaft extending from inside the telephone and sits approximately 1⁄₄ in (6 mm) above a faceplate. The faceplate is printed with letters and numbers corresponding to—and visible through—each finger hole. In North America, traditional dials have letter codes displayed with the numbers under the finger holes in the following pattern: 1, 2 ABC, 3 DEF, 4 GHI, 5 JKL, 6 MNO, 7 PRS, 8 TUV, 9 WXY, and 0 (sometimes Z) Operator. Letters were associated with the dial numbers to represent telephone exchange names in communities having more than 9,999 telephone lines, and additionally given a meaningful mnemonic to facilitate memorization of individual telephone numbers by incorporating their exchange names. For example: "RE7-xxxx" represented "REgent 7-xxxx", 'Regent' being a local exchange name used in Canada, derived from an earlier precursor telephone number, '7xxxx' –with callers actually dialing '73-7xxxx' (737-xxxx).

In the United Kingdom the letter "O" was combined with the digit "0" rather than "6". Older Australian rotary dial telephones also had letters, but the combinations were often printed in the center plate adjacent to the number. The Australian letter to number mapping was: A=1, B=2, F=3, J=4, L=5, M=6, U=7, W=8, X=9, Y=0, so the phone number BX 3701 was in fact 29 3701. However, such letter codes were not used in all countries. The 1 is normally set at approximately 60 degrees clockwise from the uppermost point of the dial, or approximately at the 2 o'clock position, and then the numbers progress counterclockwise, with the 0 being at about 5 o'clock. A curved device called a finger stop sits above the dial at approximately the 4 o'clock position.

Dials outside Canada, the United States, and large cities in Britain (before all-figure dialing) usually did not bear alphabetic characters or an indication of the word "operator" in addition to numbers. Alphabetic designation of exchanges was also used for a short period in the Soviet Union in the 1950s, but by the next decade this practice was largely discontinued.

The physical nature of the dialing mechanism on rotary phones allowed the use of physical locking mechanisms to prevent unauthorized use. The lock could be integral to the phone itself or a separate device inserted through the finger hole nearest the finger stop to prevent the dial rotating.