setting rule

noun

printing a metal strip used in the hand-setting of type in a composing stick to separate the line being set from the previous one

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012