There are two varieties of OO scale model railroad trains - American and British. The American models (referred to as American OO) are 1/76 scale, 3/4 inch (19mm) gauge, sized about half way between HO scale and S scale. The British models are made at a track gauge of 16.5mm, so they're actually HO gauge but with bodies scaled to OO (sometimes referred to as HO/OO). Most popular between 1935 and 1955, American OO scale model trains have...Continue Reading