This question doesn't have a simple or perhaps "correct" answer.
The Rugged Rails lineup began with just a few rolling stock pieces. Some, but not all, of these were smaller, 027-type cars. They initially offered a boxcar, which was a newly tooled, 027-sized car. They offered a hopper, which again was a newly tooled, 027-sized car. They offered a gondola, which was another newly tooled, 027-sized car.
Also available were a stockcar, tanker and a flatcar, all of which were the same cars made and offered previously (and still today) as RailKing cars. The flatcar came with a single car load, which was the only difference from the RailKing versions that typically came with two cars. The tanker was the single dome version, that did not have the platform around the dome. All of these cars (stockcar, tanker and flatcar) were initially made and offered, beginning in 1995. Of these cars, the tanker is probably most like a 027-type car, though it's probably not too far from scale size. The stockcar and flatcar are both semi-scale sized.
Lastly, they offered a Woodside Caboose, which was once again the same RailKing caboose initially made in 1995. This Woodside Caboose, although RailKing, and then Rugged Rails, was still a scale (or near scale) sized caboose.
Soon after the Rugged Rails separate sale cars were offered, beginning in 2001, certain items began to show up for sale under the "Rugged Rails" nameplate. From the start of these items, MTH made it clear that there would be nothing clear about what "Rugged Rails" would mean in terms of size or features.
One of the first "Rugged Rails" engines was a former Premier F59PH Amtrak diesel. Full DCS/Proto-2 electronics, full scale sized and priced at $199.95 list. Fabulous deal. Great, great sound. Tough to find today.
Another early separate sale "Rugged Rails" engine was an fantastic, PRR 2-8-0 steam engine. Near-scale sized, but unlike the "RailKing" versions that came in RTR sets and separate sale offers, this "Rugged Rails" version came with a die-cast engine AND tender! Again, full DCS/Proto-2 electronics and again, priced at $199.95! This engine is even tougher to find today, than the F59PH. To make things even more confusing (as to what MTH was thinking), the next year the same engine was offered, but with a plastic tender and the price was increased to $249.95.
About mid-decade (2005 or so), some RTR sets began to have internal components (either the engine or rolling stock) show up inside the set box with the items packaged in "Rugged Rails" boxes. I've seen the 2-8-0, 2-6-0 and 4-6-0 engines in these boxes, as well as the SW-1500 and RS-3's. But when some of these same engines are available as separate sale items, they have shown up as both "RailKing" (30-xxxx) and "Rugged Rails" (33-xxxx) items. And just to make it more confusing, I've seen "RailKing" items produced under the "Rugged Rails" part numbering system (33-xxxx).
Also making things more confusing and confounding perhaps, is that MTH has done upgrades to products through the years and sometimes the most basic offerings (RTR sets or Rugged Rails packaged items) can still come with upgraded features.
My MTH Product Reference Guides attempt to identify all of these distinctions and make some sense out of it all. Where an item is "bantam" sized or RK Scale or something in between, I try to note the differences and if a distinction is needed between what you actually get and what is noted in the catalog offer.
I'm sure this only makes more head's spin, but MTH has not made it easy. They simply don't have hard-and-fast distinctions for their "Rugged Rails" lineup. An item can be 027-sized, semi-scale or even full scale sized. Detail features can be upgraded from a prior attempt, without noting it.
I'm sure MTH simple thinks that they are offering up value, which they are, sometimes in great measures, but the buyer can't always define it from the catalog.
Sorry if this doesn't help give anyone a solid, perfect answer.
