Since the 1930s the UK toy and model railway industry has focused on the production of products on to a scale of 4mm to the foot on a 16.5mm track gauge, different from the 'scale accurate 3.5mm on the same gauge used elsewhere. This article sets out to explore the origins of this in the context of manufactured toy railways, rather than small batch and individually made 'model railways'. All too often, gauge and scale have been discussed by railway modellers as if they are a product of an exact science, rather than the result of more arbitrary factors. We suspect this may be because few knew much about toy trains and were often eager to distance themselves from them. As toy train collectors, we aim to address this.