When USA Trains first came out as Charles Ro trains originally in the 80's, there was just one series of trains. After the name changed to USA Trains, there was more product expanding to what it is today. There is now 3 different series of USA Trains and I will explain all 3 here and what the difference is. #1 The USA American series: This is a 1:24 scale ratio series product line up which was the original product line up made by Charles Ro back in the 80's. This series is not exatly the most realistic one USA Trains makes, but you don't have to worry about buying 20ft diameter curves to run any of this series on. On this series the detail parts such as grab irons and steps come in a kit bag and you install them. This series also comes with plastic wheels to further reduce costs Here is a list of American Series rolling stock that was made. 1) Woodside Box car 2) Woodside Reefer Car 3) Simulated Steel Box car not to confused with the Ultimate series 40ft box car 4) Two Tier Auto Carrier 5) All Work Series Rolling Stock 6) Ore Car 7) Piggy Back Flat Car 8) Pipe Load Flat Car 9) Woodside Caboose 10) Center Beam Flat Car The center beam flat car and piggy back flat car are no where near the correct size for the scale ratio, but USA rain captures enough in the model for people to buy and you don't need 20ft diameter curves to run a full size center beam flat car in G scale. There is no American Series locomotives at this time. #2 The Ultimate Series: "As Real AS It Gets" was USA Trains motto whe they introduced this new exciting series of more modern type rolling stock which is all 1:29 scale ratio. This is the most realistic series of rolling stock that USA Trains offers. I'm not saying they have the correct amount of rivets or brakes or exact measurements for their scale, so please no 100 responses about this is not correct or thatt is not correct for this road name. I'm just saying the Ultimate Series is USA Trains most realistic line up, as well as very detailed line up. There are alot of fragile detail parts on this series also. Here is a list of Ultimate Series rolling stock that USA Traiins makes. This series of rolling stock already has the detail parts already installed. This series also comes standarrd with a nice upgrade set of metal wheels. 1) Extruded Aluminum Passenger Car 2) Center Cupola Caboose 3) Bay Window Caboose 4) Extended Vision Caboose 5) 55ft 4 Bay ACF Hopper Car 6) 55ft Modern Tank Car 7) Depressed Center Flat Car 8) Intermodal Container Car 9) 40ft Box Car 10) 50FT Box Car 11) 40FT Reefer Car 12) 50FT Mechanical Reefer Car 13) 70 Ton 3 Bay Hopper Car 14) 10,000 Gallon Tank Carr 15) Woodchip Hopper Car 16) Intermodal 5 Unit Articulated set Locomotives 1) Dockside 0-6-0T Switcher 2) SD70-MAC 3) PA1 / PB1 4) SD40-2 5) GP-30 6) GP38-2 7) GP-7 / GP-9 8) F3A / F3B 9) S-4 Switcher 10) NW-2 Switcher 11) 44 Tonner Switcher 12) Speeder #3) The Prestiage Series: This is USA Trains newest series and is also a 1:29 scale ratio. What makes this series different is that it's made mainly from diecast metal and has alot of metal detail parts making this series the Cadillac of USA Trains. This wonderful series only has locomotives in it and includes sound. Here is a list of Prestige Series Locomotives 1) GG1 Locomotive 2) J1E Hudson 3) Big Boy Steam Locomotive Special Note: Be sure to ask the bidder o ebay to distinguish which USA Trains box car they have. I have seen many people on ebay get the America Series simulated steel box car confused with the Ultimate Sries 40ft box carr. Remember all American Series rolling stock you have to attach all detail parts such as grab irons and steps and the Ultimate series already has it installed.