A steel rule with gradations based on 1/10th of an inch on the upper and 1/16th of an inch on the lower scales.
The Line is an archaic pre-metric and pre-decimal unit of measurement, one line being equal to 1/10th or in some cases 1/12th of an inch.
In use
The Line was most useful in machining and became a standard to which small arms ammunition was manufactured. A 7.62 mm caliber round seems a numerically arbitrary round, until it is realised that 7.62 mm is 0.3 inches, .30 cal or three-lines. The Russian Mosin-Nagant rifle for example is known as the "Three-line rifle". There was also the "Four-line" Swedish 12.17 x 44 mm round, although rarely referred to as such the 12.7mm Browning HMG round is a "Five-line" round. The actual calibre of the round would differ as the actual value of the inch would vary from country to country.
References
- Military small arms of the 20th Century 6thedition, Ian V Hogg and John Weeks, Guild Publishing, 1991.
