"OW5" is not the most common reference. Most O Scale modelers do not use it. Somewhere in the dim past, 1 1/4 inches became the defacto standard for "O" size trains. Since the 1930s or earlier it has been used. There is now so much equipment using that track gauge, that it is hard to do otherwise.
Modelers who want to get more accurate track gauge, handlay their track to a scale 4 ft 8 1/12 inches and refer it to as "Proto-48".
