The models were initially built to the 1:32 scale, known in model railway circles as "Gauge 1". They used chassis made by Märklin with specially made bodies. As well as the eye mechanisms, these bodies also include smoke generators. Coaches and trucks were made using Tenmille kits. Models were later constructed entirely from scratch.
From Season 5 onwards, some larger scale models were used for the narrow gauge characters, in order to make it easier to fit the complex mechanisms into them while retaining a sufficient level of detail. In Season 6, the characters known as "the Pack" (construction machines) were also constructed to a large scale, and large models of Thomas and Percy were made to interact with them. Beginning with the ninth season, the Thomas model also interacted with the narrow gauge engines. It was joined by a large version of James in the tenth season. Then in Season 11's Engines and Escapades, large scale models of Annie and Clarabel were made to interact with the narrow gauge engines.