HO scale model trains are 1/87 the size of real trains and 1/2 the size of O scale model trains (HO stands for "half O"). As with O scale trains, the letter "O" in HO is a misnomer since the designation was initially conceived as a zero to identify trains that were smaller in scale than 1. But the use of the letter O rather than the numeral 0 crept into everyday speech among model-train buffs and remains the standard way to refer to HO scale today.

Though first invented in the 1930s, HO scale model trains didn’t become popular in the U.S. and Europe until the 1950s when the scale was heavily promoted by Märklin, Lionel, Athearn, and others. HO never quite gained acceptance in England, though, where larger 00 scale trains still predominate.

HO has two important benefits over trains of larger sizes. First, an HO scale layout of reasonably ambitious detail and complexity can fit on a table rather than requiring an entire room, as is the case with larger scales. Second, HO trains are less expensive to manufacture than OO, O, and other large-scale trains, which makes them more affordable to collectors and enthusiasts alike.

Most HO scale trains run on two-rail tracks using direct current (DC). Adjusting the voltage delivered to the tracks can increase or decrease the speed of the trains; reversing the polarity causes the trains to roll in reverse. Some manufacturers, notably Märklin, produce HO scale trains that operate on alternating current (AC), which is delivered to the train via a conductive third rail.

The gauge used by the majority of HO scale model trains is a standard HO gauge track that’s roughly proportional to the size of the trains running on top of it. But as with the OO scale trains in England that run on HO gauge tracks, HO scale trains are also made to run on a variety of different gauge tracks, which themselves are scaled-down versions of historical railroad track sizes.

Of these variants, the most common is called HOn3. This code denotes an HO scale train running on a track similar to the 3-foot, narrow gauge tracks used by Rocky Mountain railroad operators in the late 19th century.

One of the most enjoyable aspects of HO for collectors is the opportunity to join a local module club. Members of such clubs build modules of predetermined size; each module has a finite length of track. When members get together at model train exhibitions or in private homes, the modules are linked up and trains are run on the resulting massive layout, which often feels like more than just the sum of its parts.

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Airfix Model Railways

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Dave McCarthy's Airfix Model Railway treasure trove is an in-depth archive of the company's plastic railway kits fr… [read review or visit site]

Gateway NMRA

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Postwar Lionel Trains Library

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Eric's Trains

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Tech Model Railroad Club of MIT

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Recent News: HO Scale Model Trains

Source: Google News

Community Notes: March 27, 2015
Daily Astorian, March 27th

Columbia Northwestern Model Railroading Club — 1 p.m., in Hammond. Group runs trains on HO-scale layout. For information, call Don Carter at 503-325-0757. SUNDAY. Line Dancing — 5:30 to 8 p.m., Seaside American Legion, 1315 Broadway...Read more

On Tap: 'Bye, Bye Birdie' at Pittsburg High School this weekend
San Jose Mercury News, March 24th

Train show this weekend at BD Lines clubhouse. ANTIOCH -- The Black Diamond Lines Model Railroad Club hosts a show of its HO-scale train layout. from 10 a.m. until 5 p.m. Saturday an Sunday at the clubhouse at 425 Fulton Shipyard Road. For more ...Read more

Little train show a big hit
TBO.com, March 21st

The event is held to raise money for the maintenance of an HO scale model train display, DeGeorge said. The swap meet inside the museum featured donated train items sold to help with the cost of the display upkeep. The display is a representation of ...Read more

Annual Railfest at Lakeland Community College attracts model train enthusiasts
News-Herald.com, March 15th

Sponsored by the National Model Railroad Association Mid Central Region Division 5, the two-day event featured more than 100 vendors and 400 tables in six rooms including a few gymnasiums. Ten operating layouts, running the gamut from N scale, HO ...Read more

Model train open house to be held Saturday
Log Cabin Democrat, March 14th

This week, before the Train Open House, club members will re-route some tracks on the O-gauge layout for improved operation, and install circuits that will enable better control of the routes of the trains. The HO-scale layout will receive minor...Read more

Railroad Days to be hosted, appropriately enough, at Allen Train Depot
Star Local Media, March 11th

A traveling exhibit of the Dallas-Forth Worth O Scale Model Railroad Club, this 38-foot modular display is part of their permanent exhibit located at South Side on Lamar in Dallas. This year the DFW Club will be joined by modular layouts in N scale by...Read more

Model railroad builders roll into Ogden's Union Station
Salt Lake Tribune, March 7th

(Scott Sommerdorf | The Salt Lake Tribune) Riley Gardiner, and his son Miles, 3, check out a large HO scale train layout at the Hostlers Model Railroad Festival at Union Station in Ogden on Saturday...Read more

RI train expo offers something for everyone
Quad-Cities Online, March 1st

"We've graduated from Thomas to O scale, and now we're into HO. We're running the gamut." He's now a relatively new member of the Tri-County N Scale Model Train Club, which manned a huge display of the small-scale trains (1 inch to every 160 inches in ...Read more