I happened upon as I was rigging a fishing rod for my grandson. I thought these pretty round bobbers (floats, corks) should be good for something on the railroad. The next tine I was at Bass-Pro I picked up an assortment. The sizes I got are from left to right, 2 1/2”, 2”,1 1/2”, 1 1/4”, 3/4”, 1/2”. If you are as old as me you probably have plenty of medicine bottles just aching to be used. The 2 1/2” might be close to the size of one of them round tanks that has the spiral ladders for “N” gauge. You get the Idea.