Leading

In addition to the space between words and letters, it is also possible to vary the space between the lines of type. To accomplish this, metal strips of various thickness are placed between the lines. This is called leading (pronounced ledding). The metal strips, called leads (leds), are measured in points. The most common sizes are 1, 2, 3, and 4 point. Leads 6 points or more in thickness are called slugs and are cast in 6, 12, 24, and 36 point. Both leads and slugs are less than type-high and thereforedo not print.

Type that is set without leading is said to be set solid. If 10-point type is set with 1-point leading, it is set "10 on 11,'' which is indicated 10/11: the first figure indicates the type size; the second figure, the type size plus the leading. The type you are now reading is 9/11 Helvetica; that is, 9-point type with 2 points of leading.