The letter m stands for metre prototype gauge with a track width of 1000 mm.

Modern H0m trains run on realistic-looking two-rail track, which is powered by direct current (varying the voltage applied to the rails to change the speed, and polarity to change direction), or by Digital Command Control (sending commands to a decoder in each locomotive).

Ready to run models are widely available from companies like Bemo and D+R Modellbahn, a number of companies including, Lemaco and Ferro-suisse, also produced more detailed handmade brass models.

Likewise it has a following in South Africa, Japan and to a small extent Taiwan and New Zealand which also use 3'6" tracks.

In the same scale standard-gauge trains are modelled on 16.5 mm (0.65 in) gauge track, known as H0.