@Aaron G. posted:While all hobbyists appreciate the technical aspects of their respective hobbies, most of us newbies are trying to determine what the effect is in the real world - i.e., what it means for me on my setup.
I'll use myself as an example. I had HO Scale trains when I was a kid (or rather my father did). I decided to get a train for around the tree. I had see many at Disney but decided to visit the Lionel website. I chose MICKEY'S HOLIDAY TO REMEMBER" DISNEY CHRISTMAS LIONCHIEF TRAIN SET. I can't even remember why other than I wanted a Mickey set and didn't want a battery powered set. Maybe the working smoke or something.
Anyways, that was last year. So this year I wanted to expand and do some more stuff. So I start looking at the Lionel website. Ok, it says my set is O-Gauge. So You look at their website at the "Get Started" Page. They have a big graphic showing the different gauges. They don't have anything about O-Scale there. So then you scroll down and see a button to learn more about gauges. You click there and get taken to this page. You go all the way down to "O-Gauge." Its not till the end of the paragraph you get to this line:
"O-Gauge is divided into two categories: Traditional O-Gauge and O Scale."
So now that's the first time you see there is this thing called O Scale. Now you have to read fully to appreciate the differences which really are two main things:
- Higher-end products
- Larger than Traditional O-gauge products since they are more true to 1:48 scale proportions
So ok...Well how much larger? It doesn't really say. Can you use O-Scale with O-Gauge or will it look weird.
Add to this little fact. You peruse Lionel's catalog. Now I see they have an O Scale section and an O Gauge section. No problem, I just avoid O Scale. But then there are special sections (Christmas) that have both mixed in. I see something I really like. I see the CHRISTMAS LEGACY ES44AC #1224. I really want it. I miss that the catalog says O Scale and I look up the product SKU on their website. It's product SKU: 2033571. Oh, btw, they have different road numbers for this locomotive with different SKUs. So one might think the different road numbers are different gauges. Nope. But when you go to the link for either one what does Lionel have for the Gauge: O Gauge. No mention that its O Scale. You sorta figure that out when you realize the minimum curve is O52 and then look at the length of the thing.
And that's before we even start discussing whether I can use MTH or some other brand in conjunction with my O Gauge setup.
"O-Gauge" trains are any trains that run on track that is gauged at 1-1/4" between the rails. Since "O-Gauge" trains originally started out as toy trains, the "scale"of O-gauge trains can be all over the place. Most commonly it ranges anywhere from 1/48 (1/4" = 1'-0") scale to 1/64 scale (3/16" = 1'-0").
Virtually all 3-rail O-gauge trains, with their "lobster claw" couplers can be run together, regardless of their actual scale or manufacturer. Whether or not the various sizes look good together is up to the individual. Generally, toy train operators aren't too concerned with mixing scales on the layouts, while folks with more of an eye for prototype fidelity tend to run like sizes together.
Believe it or not, your Mickey's Holiday To Remember 4-4-0 American-style General locomotive with wood tender is actually larger than 1/48 scale! 
Not sure how much larger, I've never taken the time to do some measuring, calculating, and guestimating at its approximate scale, but it is definitely larger than 1/48. The boxcar appears to be a traditional-sized car, somewhere between 1/48 and 1/55 scale. The gondola and caboose maybe about the same?
Your Christmas Legacy ES44AC is listed as "O-Gauge" because it will run on O-gauge track. It may or may not be built to a true 1/48 scale. I don't own one, so I don't know. But it still may fit in just fine, looks-wise, with your current stuff. It all depends on what you think. 
