The NEM standards are defined and maintained by the Technical Commission of the MOROP in collaboration with model railroad manufacturers.
The standards cover areas like suggested grades, turnout radii, wheel profiles, coupling designs and Digital Command Control (DCC) and are mostly scale specific.
A fundamental principle in NEM standards are compromises in the exact scale reduction ratio in order to favour operational reliability of model railroad systems.
An example for this is wheel flanges which tend to be proportionally wider in smaller scales to ensure reliable operation.
In recent years, MOROP and NMRA have been working more closely together to establish common standards for developments such as DCC.