Model Railroading Glossary

This is not a complete glossary of all words, acronyms, and terms you will encounter in the world of model railroading. There are numerous others. This list represents words, acronyms, and terms I’ve looked up myself or explained to others.

AAR — Association of American Railroads. Website:

ABT — Air Brake Test. Used on prototype.

CA — cyanoacrylate /ˌsaɪ ə nəʊ ˈækrɪ leɪt/. A type of glue, also known by the brand names “Super Glue” and “Krazy Glue”.

CAT — Certified Air Technician. Used on prototype.

CLIC — Car Location Identity Code. Example: “27 03 01”, where “27” is the zone number, “03” is the track number, “01” is the spot number. See also SPINS and ZTS.

code — the height of a rail measured in one thousandths of an inch without the decimal point. Example: code 55 rail is .055 (55/1,000) inch high. In the prototype, rail size is measured in pounds per yard.

COT&S — Clean, Oil, Test & Stencil. Used on prototype.

CRB — Car Repair Billing. Used on prototype.

CUPS — Cab Unit Preservation Society. CUPS is dedicated to the preservation and operation of historic cab unit locomotives. Website:

DCC — Digital Command Control.

diesel multiple unit (DMU) — a multiple-unit train powered by on-board diesel engines. A DMU requires no separate locomotive, as the engines are incorporated into one or more of the carriages. They may also be referred to as a railcar or railmotor, depending on country. Diesel-powered units may be further classified by their transmission type: diesel-electric (DEMU), diesel-mechanical (DMMU) or diesel-hydraulic (DHMU). (Wikipedia: Diesel multiple unit)

DMU — diesel multiple unit. (Wikipedia: Diesel multiple unit)

DPM — Design Preservation Models, a brand of models.

electric multiple unit (EMU) — a multiple unit train consisting of self-propelled carriages, using electricity as the motive power. An EMU requires no separate locomotive, as electric traction motors are incorporated within one or a number of the carriages. (Wikipedia: Electric multiple unit)

EMU — electric multiple unit. (Wikipedia: Electric multiple unit)

FAQ — Frequently Asked Questions. You’ll see this used all over the Internet.

FRA — Federal Railroad Administration, part of the U.S. Department of Transportation. Website:

FRED — flashing rear end device.

FUD —  Frosted Ultra Detail at Shapeways 3D printing. Lower resolution than Frosted Extreme Detail (FXD).

FXD — Frosted Extreme Detail at Shapeways 3D printing. Higher resolution than Frosted Ultra Detail (FUD).

G scale — 1:__ scale. A reduction of size of 1:__ in the model which is equal to __ to one foot. G standard gauge uses a track gauge of 45 mm (1.772”).

gauge — the distance between the rails. Gauge is not the same thing as scale. The most common gauge in North America is 4 feet 8 1/2 inches (56.5”).

ground foam — foam rubber that has been dyed and then ground up for use in simulating various kinds of foliage in model scenery.

grade — trackage which rises (or descends) from one level to another, usually expressed as a percentage of rise. A rise of 1” in every 100” (or any other unit) is equal to a 1% grade; a 2” rise in 100” is a 2% grade, and so on. Sometimes grades are expressed as a rise of one per a number of units: a 1-in-100 rise is a 1% grade; a 1-in-50 is a 2% grade, and so on.

guard rail (bridge) — rails laid across a bridge between the regular running rails to restrain the wheels of a derailed car so that it does not go completely off the track while on the bridge.

guard rail (turnout) — short pieces of rail located across from the switch frog which pull the wheels away from the frog and guide them through the switch or turnout.

HEP — Head End Power. Used by Amtrak.

HO scale — 1:87 scale. A reduction of size of 1:87.1 in the model which is equal to 3.5 mm to one foot. HO standard gauge uses a track gauge of 16.5 mm (0.649”). When the scale for HO was set many years ago, O scale models were built to a scale of 7 mm to the foot. So HO was “Half O” or 3.5 mm to the foot.

interchange — one or more tracks used to exchange cars between railroads. On a model this is an easy way to generate traffic as well as to provide a connection from the model to the rest of the world.

intermodal — equipment designed to be used by more than one mode of transportation, most commonly rail, water and road.

Kadee couplers — a proprietary system of couplers in several scales allowing automatic coupling by pushing cars together and magnetic uncoupling. Micro Trains produces the same couplers in N scale. These have been the couplers of choice of most serious modelers for many years. Since Kadee’s patents ran out recently, there have been a number of imitators or clones on the market.

kitbash — altering the parts of a kit to produce a car or structure that is unique, or combining parts from two or more kits to produce a car or structure that is unique.

LHS — Local Hobby Shop.

Liquid Nails — a proprietary brand of panel adhesive sold in tubes to be used with a caulking gun.

Micro-Trains couplers — see Kadee couplers.

MOW — also MoW. maintenance of way. Used to maintain the track and track structure of a railroad.

N scale — 1:160 scale. A reduction of size of 1:160 in the model which is equal to 1.9 mm (0.075”) to one foot. N standard gauge uses a track gauge of 8.97 mm (0.353”). The letter “N” was chosen because N standard gauge track had the rails laid 9 mm apart and since the scale originated in Germany, the N signifies “neun” in German (“nine” in English). The gauge has since been changed to 8.97 mm (0.353”).

NMRA — National Model Railroad Association. Website:

NMRA Gauge — a track gauge that also has a number of other uses for checking wheel and track relationships. In most gauges it can also serve as a clearance gauge.

O scale — 1:48 scale. A reduction of size of 1:48 in the model which is equal to 1/4” to one foot. O standard gauge uses a track gauge of 1.250”. At one time O scale was the most popular size for modelers, but it was surpassed by HO scale during World War II.

PICL — Perpetual Inventory Car Location. Pronounced “pickle”. Precursor to the Southern Pacific Industrial Numbering System (SPINS).

pin vice — a handheld device used to hold very small drill bits, files and other very small tools while working on a model.

points — the movable rails of a turnout or switch.

Proto:87 — a group that models track and wheels to exact scale in HO. NMRA Standards are somewhat oversized to allow for more reliable operation of model trains on track that is built to less exacting standards. Website:

prototype — the real thing. That from which we are making our model.

PTC — Positive Train Control.

railway post office — a car built by the railroad to standard postal designs and leased to the United States Postal Service in which one or more postal clerks picked up, sorted, and delivered mail while the car was enroute between two cities.

Recommended Practice — a practice not absolutely essential to interchange of models between modelers and their layouts, however, it is recommended by the NMRA for use by all modelers and manufacturers.

rolling stock — freight, passenger, and MOW cars. Equipment designed to roll on the track. Does not include locomotives.

RP — see Recommended Practice.

RPO — see railway post office.

RTR — ready-to-run. Rolling stock that can be taken from the box and placed directly on the track with minimal (if any) assembly by the modeler.

S scale — 1:64 scale. A reduction of size of 1:64 in the model which is equal to 3/16” (0.188” or 4.76 mm) to one foot. S standard gauge uses a track gauge of 0.875” (22.2 mm).

scale — the ratio of the size of the prototype to the size of a model. Scale is not the same thing as gauge. Example: 1:160 scale (N scale) is 1 real world (prototype) inch equal to 160 inches in N scale.

scale mile — a real mile scaled down in the same proportion as the model. An N scale mile is 33.0 feet; an HO scale mile is 60.7 feet; an S scale mile is 82.5 feet; and an O scale mile is 110.0 feet.

SOP — Standard Operating Procedure. Quite often used derogatorily.

SPINS — Southern Pacific Industrial Numbering System. Example: “27 03 01”, where “27” is the zone number, “03” is the track number, “01” is the spot number. See also CLIC and ZTS.

staging (trackage) — used to store complete trains off of, or away from, the layout, from which they can be run into the operating area and to which they can be returned and stored when they are no longer needed. Staging is commonly hidden. Staging usually represents places well outside of the layout’s depicted area so that trains may be considered to run from some place well beyond the basement onto the layout and then to continue on to someplace else beyond the basement.

stock rail — the continuous rails of a turnout that are an extension of the original two rails in front of and continuing down the outside on either side of the turnout.

throw bar — the narrow bar which joins the rails at the points of a turnout which allows the switch to be “thrown” from one side to the other. It normally has an extension which allows a ground throw or switch machine to be attached at the side and a hole at the middle for an under-table mounted switch machine.

track gauge — a device used to set and maintain the proper distance, or gauge, between the rails.

traction — general term for electrically propelled street cars (trolley cars) and interurban cars.

trucks — the assembly of wheels, axles, bolster and side frames that provides the rolling portion of a car or diesel locomotive.

tunnel motor — … ( “Tunnel Motors, The SD45T-2 And SD40T-2”)

turnout number — the ratio of the number of units along the center line of a switch frog traversed for each unit the frog spreads to the sides. A No. 4 frog diverges 1 unit for every 4 it moves ahead; a No. 6, 1 for every 6 units. Although we usually refer to a turnout or switch number, in reality the measurement is for the frog.

U-boat — …

UMLER — Also Umler. Universal Machine Language Equipment Register.

USRA — United States Railroad Administration, the nationalized railroad system of the United States between 1917 and 1920.

vertical curve — the curve assumed by the track as it changes from level to a grade or vice versa.

wing rail — the portion of the closure rail which is bent to extend past the frog.

yard — an assembly of tracks within defined limits used for the purpose of breaking down arriving trains, storing cars, and making up departing trains. There may also be tracks for special purposes such as cleaning cars, repairing them, and servicing locomotives.

Z scale — 1:220 scale. A reduction of size of 1:220 in the model which is equal to 0.055” (1.39 mm) to one foot. Z standard gauge uses a track gauge of approximately 1/2” (0.250”). Z scale is the smallest practical model size in mass production.

ZTS — Zone–Track–Spot. Used by Union Pacific, Conrail and others. Example: “04 829 02 03 HINDA-DIST”, where “04” is the Zone, “829” is the Track, “02” is the beginning Spot, “03” is the ending Spot, and “HINDA-DIST” is the customer. See also CLIC and SPINS.