"HO" means "half - o;" models are half the size of O Scale. HO is the most popular scale with the greatest selection of sets and accessories, as it allows lots of railroad action in a small area. Children may need adult help to set up or take down the set.

S Scale trains appeared in the 1950s (American Flyer was one of several popular brands) as houses grew smaller. Its chief advantage was size; larger than HO for more detail and improved reliability, but smaller than O Scale so less room was needed for a layout. Today, the selection of kits and assembled items is small, but this has made S Scale popular with modelers who enjoy the challenges of scratchbuilding and kitbashing.

O Scale trains also include "On30" Sets, which are O Scale models that run on a narrower track -- just 30 scale inches wide. They're ideal for use with Christmas Villages. "O27" gauge sets will take tighter curves -- which makes these O Scale sets a good choice when space for bigger trains is limited. (The number 27 refers to the 27" diameter of a full circle of track.) If you grew up with Lionel trains, you'll remember that they were O Scale models. Ruggedly built, they're a good choice for youngsters or permanent layouts. Many sets feature animated accessories.

Big models, sometimes called "Large Scale" trains. Sizes range from 1/22.5 to 1/25 and also includes #1 gauge (1/32 Scale) equipment. The largest electrically powered models, starter sets set up in small areas. Some brands can be used outdoors, in garden layouts. The large size of G-scale trains allows for rugged handling by younger children. Many models have working parts that enhance play value.