Not in use these days - this is a portion of the bolter - the device used to sift flour into different grades of fineness. The horizontal arrangement of wood was wrapped in silk of varying weave, finer at this end, and coarser at the far end to the right (this thing is about 15 feet long). As the whole thing rotates (driven by belts and pulleys connected to the mill's main drive train) flour is added inside the rotating cylinder from the chute visible on the left next to the center shaft. the finest flour would fall through the silk here, courser flour woth move down to the other end (the whole was on an incline). Once the flour collected below, an auger would push it along horizontally, where each grade would fall through holes in the bottom to be collected in different sacks.