First appearing in 1995 and now encompassing more than 5,000 items, RailKing is M.T.H.'s bestselling and most attractively priced product line. Cars and locomotives featured in the M.T.H. RailKing line are equipped with moderate detail and run on the same O gauge track as the intricately detailed O scale models found in our Premier Line. But, because RailKing models are shorter in length, they can negotiate tighter curves.RailKing enginess are shorter in length, and can negotiate tighter curves. In fact, most RailKing models can negotiate a circle as small as 31 inches in diameter, and some can operate on curves even smaller than that. This is a real advantage for model train enthusiasts with modestly sized layouts. Over the years, the RailKing line has evolved into three subcategories: RailKing, RailKing Scale,and RailKing Imperial. RailKing Imperial locomotives retain traditional proportions and O-31 minimum curve operation like regular RailKing locomotives, but are equipped with a level of detail usually found only on more expensive, full-scale engines that require much larger curves. RailKing Scale diesels are full scale-proportioned models featuring a higher level of detail than that found on regular RailKing models. Because of their scale proportions, RailKing Scale models require a minimum of O-31 curves in order to operate.