There are three common slot car scales (sizes): 1:24 scale, 1:32 scale, and HO size. 

In 1957, Minimodels converted its Scalex clockwork models to electric, creating the Scalextric line of slot car models, and Victory Industries (VIP) line, both companies eventually using the plastic to provide controllable slot cars in 1:32 scale for the mass market. Both included versatile track for home use or competitive events.

As Scalextric became more popular in the UK, American manufacturers  Aurora Plastic Corp. released HO scale cars with success in the USA. The tiny cars intrigued the public, and their cost and space requirements were better suited to the average consumer than the larger 1/32 and 1/24 scales.