They feel like clay or some sort of concrete. They're all the same size at about 3 1/2 inches in diameter and 4 inches tall. I would love to believe that they're some sort of column components, but being so small, I'm doubtful. They were all found in a fill layer along some railroad tracks, but it's in Northwest Indiana in a hugely industrial part of the state, which is why I'm assuming they had to come from a factory or something like that. And yes, the canals run all the way through the pieces, both circular ends look exactly the same. I like the corn sheller/mill idea, because corn plays a huge part of the local economy as well.