What is "guide bar"

Guide \Guide\, n. [OE. giae, F. guide, It. guida. See Guide, v. t.]

1. A person who leads or directs another in his way or course, as in a strange land; one who exhibits points of interest to strangers; a conductor; also, that which guides; a guidebook.

2. One who, or that which, directs another in his conduct or course of life; a director; a regulator.

   He will be our guide, even unto death.
   --Ps. xlviii. 14.

3. Any contrivance, especially one having a directing edge, surface, or channel, for giving direction to the motion of anything, as water, an instrument, or part of a machine, or for directing the hand or eye, as of an operator; as:

   1. (Water Wheels) A blade or channel for directing the flow of water to the wheel buckets.

   2. (Surgery) A grooved director for a probe or knife.

   3. (Printing) A strip or device to direct the compositor's eye to the line of copy he is setting.

4. (Mil.) A noncommissioned officer or soldier placed on the directing flank of each subdivision of a column of troops, or at the end of a line, to mark the pivots, formations, marches, and alignments in tactics.
   --Farrow.

   Guide bar (Mach.), the part of a steam engine on which the crosshead slides, and by which the motion of the piston rod is kept parallel to the cylinder, being a substitute for the parallel motion; -- called also guide, and slide bar.

   Guide block (Steam Engine), a block attached in to the crosshead to work in contact with the guide bar.

   Guide meridian. (Surveying) See under Meridian.

   Guide pile (Engin.), a pile driven to mark a place, as a point to work to.

   Guide pulley (Mach.), a pulley for directing or changing the line of motion of belt; an idler.
   --Knight.

   Guide rail (Railroads), an additional rail, between the others, gripped by horizontal driving wheels on the locomotive, as a means of propulsion on steep gradients.

The rubber-tyred metro systems that incorporate track have angle irons as guide bars along the roll ways. The Busan Subway Line 4, that lacks a rail track, has I-beams installed with the flanges being vertical. The Sapporo Municipal Subway, that lacks a rail track as well, has none.