Bowker 2-4-0 Steam Engine
Genoa 4-4-0 Steam Engine
Reno 4-4-0 Steam Engine
Casey Jones 4-6-0 Steam Engine
Inyo Steam Engine
Baldwin American Steam Engine
Hudson J3a 4-6-4 Steam Engine
Streamlined Hudson Steam Engine
Big Boy 4-8-8-4 Steam Engine
Northern 4-8-4 Steam Engine
Challenger 4-6-6-4 Steam Engine
Heisler Steam Engine -Two Truck
Heisler Steam Engine -Three Truck
Berkshire 2-8-4 Steam Engine
A-3 Switcher Steam Engine
Mikado 2-8-2 Steam Engine
Smoking "Big Mikes" 2-8-2 Steam Engine
Heavy Pacific 4-6-2 Steam Engine
C&O F-19 Pacific 4-6-2 Steam Engine
Simplified Pacific 4-6-2 Steam Engine
Light Pacific 4-6-2 Steam Engine
Dockside 0-4-0 Steam Engine
Booster 0-4-0 Steam Engine
Saddle Tank 0-6-0 Steam Engine
0-6-0 Steam Engine
USRA 0-6-0 Switcher Steam Engine
Shifter 0-4-0 Steam Engine
Switcher 0-8-0 Steam Engine
"Santa Fe" Class S-1 2-10-2 Steam Engine
USRA Mallet 2-8-8-2 Steam Engine
2-8-8-0 EL-3 Mallet Steam Engine
Santa Fe Blue Goose Steam Engine
Cab Forward 4-8-8-2 Steam Engine
C&O L-2 Hudson Steam Engine
Brass Locomotives
Simulated Gold Locomotives
French Pacific
Trevithick's 1804 Locomotive kit
Kitmaster Kits
ALCO 1000
ALCO Century 424
ALCO Century 420
ALCO Century 628
ALCO RS-2 Powered & Dummy
GE 35 Ton Switcher
GE Center Cab
GG-1 Electric
EMD SW1 w/Brakeman and Light
EMD FP45 -Yugoslovia
EMD FP45C -Lima
EMD GP18 w/Flashing Beacon
FM C-Liner
FM C-Liner B-Unit
Krauss Maffei
Plymouth MDT Switcher
Boeing LRV Trolley
Birney/Brill Trolley

2-8-8-2 Y6B Mallet Steam Engine
Norfolk & Western
No. 5092 -1965 Release
No. 5090-D
No. 5092-B -1977 Release with .039 flanges
No. 17511

2-8-8-2 Y6B Mallet Steam Engine
Pennsylvania Railroad
No. 5090

2-8-8-2 Y6B Mallet Steam Engine
Santa Fe
No. 5091
No. 5090-C
No. 17512

2-8-8-2 Y6B Mallet Steam Engine
Simulated Gold
No. 5093 -$55.98

2-8-8-2 Y6B Mallet Steam Engine
No. 5092-C -1977 Release with .039 flanges 

AHM 2-8-8-2 Y6b

AHM adds its Norfolk & Western Mallet 2-8-8-2 Y6b in mid-1965. The original asking price for the Rivarossi-made steam engine was $39.95.

Click to View Larger Image

Today's HO-scale modelers probably give no thought to the depth of the flanges on wheels. As you'll see in this 1977 ad from AHM, flanges were becoming an issue as the HO-scale market continued to get more serious and prototypically concerned. Many of AHM's releaes up to this time featured deep flanges with a .050 measurement. Generally, it was the Rivarossi made releases that suffered from the deep flange issue. As noted, this 1977 re-release of the impressive N&W Y-6B Mallet was an experiment for AHM to gauge reaction to smaller .039 flanges.
What's the difference? The deep flanges are a non-issue on Code 100 HO-scale track, but attempt running an older loco with deep flanges on Code 83 track and you'll see and hear the problem. The deep flanges will bump along on the ties, as the more accurate high Code 83 track is not tall enough to clear the flange height.

Image sources include AHM product catalogs and advertisments, as well as images from eBay auctions and other sources. Information presented comes from variety of sources including product catalogs, magazine articles and Wikipedia.