Prototype trains of the US, Canada, Mexico, and Europe operate on standard gauge track which is 4 feet 8 1/2 inches.
O gauge track is 1 1/4 inches between the two outside rails (ignoring the center rail).
At 1:48 scale (1/4 inch scale), O gauge track works out to be 5 foot gauge.
At 1:45 scale (17/64 inch scale), O gauge track works out to be 4 feet 8 7/16 inches; very close to that of standard gauge.
At 1:43.5 scale, O gauge track works out to be roughly 4 feet 3 inches.
17/64 inch scale is the most accurate scale for O gauge track. In fact, Lionel's first scale models back in the mid 1930's were 17/64 inch scale. Calculate every dimension by 17 and then divide by 64 by hand and you will soon find out why Lionel soon went to 1/4 inch scale. Dividing by 4 is a whole lot easier. 17/64 inch scale is still considered O scale and many publications describe 17/64 as the more accurate version of O scale.
A way one could look at it is that MTH's model is too small for O gauge track while Lionel/K-Line model is too large for O gauge track by just about the same proportion.
