These models are sold in 5-unit articulated sets. Containers sold separately.
Generally speaking, Deluxe Innovations split production of their models between the US and China (just how much of what was done where varies by model and production run). DI went out of business in 2017 and the tooling for these cars was subsequently acquired by Fox Valley Models in 2018.
Here's what Deluxe had to say about them -
First developed in the early 80's, the Twinstack was the first double stack car to become popular with a number railroads. The five unit articulation concept was used to reduce weight and coupler slack. Why five units? Santa Fe had used 10 unit spine cars since the seventies but since one bad section bad-ordered the whole set, 10 units meant the car was out of service too much. Five units provided the perfect ratio of cost savings to down time. The bottom position of each well will accommodate one 40' container or two 20' containers. Some railroads ordered their cars to handle 20 footers only on the two end wells while other railroads opted for 20 footers on the only the middle three wells. The difference lies in whether "hard points" were attached in the middle of the well to support the ends of the 20' containers. The upper position will hold 40', 45', or 48' containers. Twinstacks belonging to SeaLand had extra attachment points so that company's proprietary 35' containers could be carried in either position. The large bulkheads at the ends of each well were designed to hold the top container in place. Even these large structures were sometimes not enough in high winds as empty containers were known to blow off. To stop this rash of un-piloted flying cargo boxes, some cars were equipped with 8' high walls that were welded to the tops of the bulkhead. Hoping this would deflect the problem with the wind, the empty car now stood more than 20' tall! Before the success or failure of this technique could be judged, it became a moot point when someone realized that the InterBox Connectors (IBC's) that locked containers together on ships could be used on trains too. Seemingly overnight, the bulkheads became nothing more than decoration. Gunderson's subsequent double stack designs had no bulkheads. Ironically, the Twinstacks are so rigid that only a couple of wrecked cars have been retired with the rest of the fleet intact and in operation to this day.
We set out to push the envelope on this model. The car is ready to run with free standing brake detail and scale sized open lattice floors. The distinctive circular depressions on the inside faces of the side sills are accurately reproduced. The end platforms and grab irons are made of etched stainless steel to better reproduce the open gridwork of the prototype. The model is semi-permanently coupled together to make handling and railing the car easier. The model is designed to run partially or fully loaded and container weights are included. If the car is to run empty, we follow the guidelines of the prototype, and suggest that you run it at the end of the train. The car halves are assembled with steel pins in the bolster boxes, as that is the only place that one could hide weight. Thank goodness it's right over the trucks! Make sure all of the articulators are free and loose, and away you go!
Containers that will fit the wells include -
Lower position - deLuxe innovations 20 foot, Roco 20 foot, deLuxe innovations 40 foot reefer, deLuxe innovations 40 foot corrugated dry box, MicroTrains rib side dry box, Walthers Hi Cube corrugated dry box, and Roco 40 foot smoothside.
Upper Position - deLuxe innovations 48 foot reefer, deLuxe innovations 48 foot Monon smoothside, Walthers 48 foot Stoughton rib side, ConCor 48 foot rivet side, deLuxe innovations 40 foot reefer, deLuxe innovations 40 foot corrugated dry box, MicroTrains 40 foot rib side dry box, Walthers 40 foot Hi Cube corrugated dry box, and Roco 40 foot smoothside.
There are some older prototypes that are out of scale. DO NOT try to force these containers in to the car, as the car will split. The lower well of the car is a tight fit for scale containers. The outsize boxes will split the sides of the car and cause permanent damage. Containers can be firmly installed and removed over and over again by using deLuxe innovations Container Glue. Roll up a tiny snake and place it in the ribs on the bottom of the container, press it firmly into the top of the next container, and it will hold it's position without damage or marking until you move it. This gummy substance has been tested on all kinds of containers and does not remove or mark paint that has been properly applied. Container Glue can be used on all brands of well cars, and is great for routing simulations and loads out/ empties back operating schemes.