In 1972 LEGO released the 4.5V and 12V train sets as part of the Blue Era which was named because of the rail color. These train sets used additional conductor rails mounted between the standard 4.5V rails and 12V motors contained in the same housings as the 4.5V motors, but with additional metal contacts attached to the bottom of the housings.
1975 LEGO Sets
In 1975, LEGO continued to expand its product range with a variety of new sets and themes. This year saw the introduction of the LEGO Basic Building Set, which provided builders with a selection of standard bricks in various colors and shapes, along with instruction booklets containing building ideas. These sets reinforced LEGO’s core concept of open-ended creativity and served as the foundation for many future builders.