Hi, I've got many passenger cars with 3 wheel sets that drove me nuts till i came up with a way to set the width and align them all in one shot. Inspecting all my Bachmann engines i measured the width inside the flanges .562 seems to be the number which coincidentally equal 9/16's of an inch.
You can find 9/16 Th's square stock or even a drill rod for the job. I made mine about 2 inches long out of square stock, seems to do the job well. Just remember most wheel sets have one fixed wheel and one pressed on wheel or plastic bushed for electrical isolation. Put the wheel sets into the truck keeping the fixed wheels to one side and place the tool between the flanges if you get a slight drag pushing it though between the flanges it's perfect and no more derailments.
Have Fun
You can find 9/16 Th's square stock or even a drill rod for the job. I made mine about 2 inches long out of square stock, seems to do the job well. Just remember most wheel sets have one fixed wheel and one pressed on wheel or plastic bushed for electrical isolation. Put the wheel sets into the truck keeping the fixed wheels to one side and place the tool between the flanges if you get a slight drag pushing it though between the flanges it's perfect and no more derailments.
Have Fun