Lines of type are easier handled by the aid of a composing rule. It is not practicable to set small types in the stick without some support or to set a second line immediately next to another without a lead or rule to separate them. The composing rule furnishes a smooth surface against which to place the types as they are assembled and to keep them in line while the respacing and justifying is done. The rule is also convenient for lifting lines out into the galley and for handling them in later operations.

Sets of these rules can be purchased from supply houses or they may be made from a discarded strip of brass rule (2-point or 3-point), by trimming one end so as to leave a nib 10points long.

Composing rules are not used now as much as formerly, owing to the fact that hand composition is largely in the nature of job work. A compositor in a day sets a great variety of line-lengths, many of them in large types, and he dispenses with the composing rule as a needless tool, using instead the ready-at-hand leads and slugs needed for the page. In many cases this is advisable. Yet when there are many lines of one length to set and to correct and later to make up into pages, the composing rule is recommended as a useful accessory.