--RailKing Scale: Former Premier diesels whose detailing is no longer considered Premier-grade (1990's - early 2000's tooling). All will negotiate 031, typically by having undersized fuel tanks. No Premier steam engines ever entered this product line.
--RailKing Imperial: RailKing 'traditional'-sized steam with upgraded detail. Basically all but the largest non-articulated examples will negotiate 031 curves. Diesels with an Imperial designation have added details and/or features typically left out of other RK examples, such as working ditch lights.
--RailKing Rugged Rails: first-generation RailKing locomotives that were really undersized, like the first-generation F3 and Dash-8, plus the 'Bantam' steamers like the N&W J-class and PRR turbine. Rugged Rails was a product line that appeared some time after the creation of RailKing, as a sub-category of budget offerings typically included in entry-level starter sets.
---PCJ
