The line (abbreviated L or l) was a small English unit of length, variously reckoned as 1⁄10, 1⁄12, 1⁄16, or 1⁄40 of an inch. It was not included among the units authorized as the British Imperial system in 1824.
Contents
Size
The line was not recognized by any statute of the English Parliament but was usually understood as 1⁄4 of a barleycorn, which itself was recognized by statute as 1⁄3 of an inch but often reckoned as 1⁄4 of an inch instead. The line was eventually decimalized as 1⁄10 of an inch, without recourse to barleycorns. The button trade used the term, redefined as 1⁄40 of an inch.
In use
Botanists formerly used the units (usually as 1⁄12 inch) to measure the size of plant parts. Linnaeus's Philosophia botanica (1751) includes the Linea in its summary of units of measurements, defining it as "Linea una Mensurae parisinae"; Stearns gives its length as 2.25 mm. Even after metrication, British botanists continued to employ tools with gradations marked as linea (lines); the British line is approx. 2.1 mm and the Paris line approx. 2.3 mm.
Gunsmiths and armament companies also employed the 1⁄10-inch line, in part owing to the importance of the German and Russian arms industries. These are now given in terms of millimeters, but the seemingly arbitrary 7.62 mm caliber was originally understood as a 3-line caliber (as with the 1891 Mosin–Nagant rifle). The 12.7 mm caliber used by the M2 Browning machine gun was similarly a 5-line caliber.
Foreign units
Other similar small units called lines include: