The LEGO 4.5V train theme ran from 1966 until 1971 and contained 39 sets in all. The 4.5V trains used to be the voltage standard for the first electric LEGO components where the power came from a battery box with 3x 1.5V batteries.
1967 LEGO Sets
In 1967, LEGO began to better define and redefine how LEGO sets were scaled. This was an important change that we still see in modern LEGO sets today. During the 1960’s the size of LEGO sets and scale of the models had changed, mostly growing larger over time. With the mid 60's introduction of model sets, known as Model Makers in the US, these sets were based, not on the 1:87 scale of the Town Plan, but on the larger scale of the 2 x 2 wheel. The train sets introduced in the previous year and a series of truck models in 1967 were also designed around the 2 x 2 wheel and from that point on all new development was based on this larger scale. The LEGO System had changed from the loosely scaled Town Plan to a larger, and much more consistent, scale. A scale that integrated nearly all the sets and one that is close to the mini-fig scale of today.