Main Line (Main Iron, Main Stream, etc.)
Through trackage; governed by rules and restricted to travel only by scheduled trains or trains operating with train orders.

Main Pin
Slang term for a railroad official.

Maintenance-of-Way Equipment
Machinery and rolling stock used to keep track and roadbed in good operating condition.

Mallet
An articulated steam locomotive named for the designer. The term is generally applied to any articulated steam locomotive.

Manifest
A listing or invoice-of-charge for a particular shipment of goods or materiel.

Markers
Lamps displayed on the rear of a train to indicate that the complete train has passed, or to serve as a warning to following trains.

Milk Train
A slow train.

Modular Layout/Modular Railroading
A type of model railroad layout in which the layout itself is comprised of portable modules constructed to specifications that permit each module to be joined to others, thereby creating a large layout limited only by space and number of modules available.

Mother Hubbard
A locomotive with the cab straddling the boiler like a saddle. See also "Camelback."

MTY's
Empty freight cars.

MU (Multiple Unit)
Cars or locomotives which contain their own power, but which can be controlled from the foremost car or locomotive; commonly used on commuter trains and diesel locomotives.

Mule
Slang term for brakeman.

Muzzle Loader
Any hand-fired steam locomotive.

N Scale
Model railroad scale in the proportion of 1:160. The second most popular (after HO Scale) of the model railroad scales in use today.

Narrow Gauge
Term designating railroad track having a rail spacing (gauge) of less than the North American standard of 4 feet, 8-1/2 inches--typically mining, industrial, and scenic railways which most commonly have rail spacing of either 3 feet or 2 feet. In model railroading, narrow gauge is designated by the modeling scale, followed by an "n" (narrow gauge), and then the modeled track gauge--for example, On3 or HOn2.

Nipper
Slang term for brakeman.

NMRA
National Model Railroad Association. A national organization dedicated to the advancement of model railroading in all scales. The organization instrumental in the establishment of standards for model railroading. For membership information, write to: 4121 Cromwell Road, Chattanooga, TN 37421.

Nose
Front end of a locomotive.

NRHS
National Railway Historical Society. Organization dedicated to the perpetuation of prototype railroad history. For information, write to: 1 Rich Court, HoHoKus, NJ 07423.

Number Grabber
A car checker.

Nut Splitter
Slang term for a machinist.

O Scale/O Gauge
Model railroad scale in the proportion of 1:48 (nominally, 1/4 inch = 1 foot); includes O scale, O gauge, O27 gauge, and On3 and On2 scale model trains and equipment. The standard track gauge for O/O27 measures 1-1/4 inches between the running rails.

Off-Line
When a railroad's equipment that is normally limited to operation in home territory--locomotives and business cars, for example--is operated over the trackage of another railroad.

Ohm
In electricity, the fundamental unit of electrical resistance. It is a measurement which describes the resistance of a circuit to the flow of electricity passing through it. A greater number of Ohms indicates a higher resistance, or impediment, to current flow.

"On-the-Advertised"
Railroading term for running on time.

Open-top
or
Oil Can
Slang term for a tank car.

Open-top
or
Open-Grid Layout
A type of layout design which uses a wooden frame with joists, thereby allowing the roadbed to rise and fall beneath the top level of the frame by means of cross members and strips of wood called stringers.

O27 Gauge
Toy train track which has the same distance between the outside running rails as O Gauge (1-1/4 inches), but is lighter in weight, has a lower profile, and measures only 27 inches over the diameter of a full circle. Also, the term applied to O27 trains, which generally are shorter or somewhat smaller than their true O Gauge counterparts--made so to negotiate the smaller-radius curves.

OS
Means "entered on the sheet." Often used as a verb to report that a train has passed the tower.

Paddle
A semaphore signal.

Palace
Caboose.

Pantograph
The collapsible, adjustable, "floating" structure which provides electrical contact with overhead wires on an electric locomotive, so-called for its pivoting capability.

Parallel Circuit
In electricity, a single electrical circuit serving several electrical devices (such as lamps), each of which is connected directly to both poles of the power source. All devices in the circuit will receive the full amount of electrical voltage available from the two poles. (See also Series Circuit).

Passing Siding
A siding intended specifically for passing complete trains in the same or opposite direction.

PCC Car
Abbreviation for "President's Conference Committee" streamlined-style streetcars and interurbans produced from the mid-1930s through the mid-1940s.

Peddler
See "Way Freight."

Phase
or
Phasing
In model railroading, the connection of two or more transformers in such a way that the continuous movement of alternating current (AC) in all of the transformers from positive to negative is identical. Two transformers that are "Out of Phase" can be corrected by rotating the wall plug of only one of them 180-degrees.

Pickup Roller
A device mounted on the underside of a toy train car or locomotive which contacts the third (center) rail to supply electrical power to the motor(s) or lamp(s).

Pier
A support for the center section of a bridge.

Piggyback
The movement of truck trailers on flat cars. See also, "Intermodal."

Pike
A model railroad layout.

Pilot
Correct nomenclature for the guard structure at the front of a steam locomotive; often called a "cowcatcher."

Pilot Truck
(Also lead or leading truck). The truck located in front of a steam locomotive's drive wheels which, in addition to providing support, helps guide the engine into curves and turnouts. See also "Pony Truck."

Plug
A small, local passenger train.

Polarity
In electricity, the condition of either positive or negative magnetic or electrical attraction which cause current to flow.

Pole
In electricity, each of the two opposing parts of a battery or other power source which exhibit attraction for each other, thus inducing a flow of electric current.

Poling
Moving cars on an adjoining track by using a long wooden spar placed in a socket on the car's end beam and a socket on the locomotive's pilot beam.

Pony Truck
A two-wheel pilot truck on a steam locomotive.

Pop Car
Motor car used by section gangs.

Pot
Locomotive.

Power Pack
In model railroading, normally a train control device configured to convert household AC current to low-voltage DC current which is used for the operation of most model trains that run on two-rail track.

Primary Coil
The lighter wire winding in the core of a toy train transformer that connects directly to the household electrical supply by means of a wall plug. See also, Secondary.

Prototype
The real, life-size object on which a scale model is based.

Pullman
A sleeping or parlor car operated by the Pullman Company; also commonly applied to any car of that same type.

"Rail"
Slang term for a model railroader.

Railfan
An individual who enjoys riding, watching, photographing, and reading about trains.

Rat
Slang term for a freight train.

RCS (Remote Control Section)
A special type of Lionel track used for uncoupling and unloading cars through activation of an electromagnet by remote control; replaced by the designation "UCS."

RDC (Rail Diesel Car)
A lightweight, self-powered commuter and/or mail-carrying car often operated in multiple units; manufactured by the Budd Company.

Rectifier
In electricity, a device used to transform alternating current (AC) into direct current (DC). May be used with an AC-type transformer to power equipment which requires DC current. See also, Power Pack.

Red Ball
Fast freight train.

Red Eye
or
Red Board
A "stop" signal.

Reefer
Slang for a refrigerator car.

Reefer Block
Freight train consisting of refrigerator cars.

Relay
In electricity, an electrically-powered switch which, in turn, effects a change (activates other switches) in some other electrical circuit or circuits.

Resistor
In electricity, a device which impedes current flow, thereby reducing the voltage passing through a circuit; resistance is measured in ohms.

Restricted Track
A track section where train speeds are reduced by orders, often temporarily.

Retarder
A device used for decreasing speed; often used in hump yards to control the rate at which cars roll down the hump and into the classification tracks.

Rheostat
In electricity, a device for adjusting the amount of resistance in an electrical circuit, thereby varying the amount of voltage produced in that circuit.

Right-of-Way
The track, roadbed, and property alongside which is owned by the railroad.

Ringmaster
Slang term for yardmaster.

Rip Track
Track in a yard where equipment is stored while awaiting repairs, or where minor car repairs are performed.

Road Railer
A specially designed over-the-road truck trailer having a set of steel railcar-style wheels which can be lowered for running on train tracks or designed to rest on a two-axle bogie similar to a freight car truck. The front end of the trailer is supported by being hitched to the back of the one in front--literally making a train of truck trailers.

Roadbed
The surface upon which track is laid. This surface is usually raised above ground level by rocks topped with wooden or concrete ties, upon which the tracks are laid and then ballasted.

Road Engine
Locomotive used regularly for mainline passenger or freight service.

Rolling Stock
Non-powered freight and passenger cars which are pulled by a locomotive.

Roundhouse
A circular (usually) structure meant to house locomotives during servicing. The roundhouse customarily faced a turntable which was used to direct a locomotive onto and off of one of the roundhouse tracks.

RPO
Railway Post Office car. Once a common addition to passenger trains.

Runaround
A railroad switching maneuver in which the locomotive uncouples from its train, pulls ahead, backs past on an adjacent track, and moves forward to couple onto the rear of the train. Also, the track where such movements take place.

Running Board
The narrow walkway alongside the boiler of a steam engine.