Individual track and scenery modules are built to a common standard and are joined together to make larger model railway layouts.

Track uses Code 83 rails (2.1 mm or 0.083 inches high), with a minimum curve radius of 2,000 millimetres (6 ft 7 in; representing 175 metres or 575 feet at 1:87) and fixed track centre-line spacing of 46 millimetres (1.8 in; representing 4 metres or 13 feet separation at 1:87 scale).

[2] Some general aspects, such as rigid construction of modules, are derived from the Normen Europäischer Modellbahnen NEM 900 standards published by MOROP.

[4][1] In 1994 Chris Palomarez and Art Armstrong at the San Luis Obispo Model Railroad Club (SLOMRC) developed the Free-mo Standard based on the European FREMO concept.

In 2011 the NMRA British Region released a set of standards called Freemo, Recommended Specifications For HO Scale Modules.