Cleaning and conditioning having been attended to, the grain is now conveyed to the mill proper. This of course is done by a mechanical arrangement which feeds the grain at any desired rate into the hopper which supplies the first pair of rolls. These rolls consist of a pair of steel cylinders usually 10 inches in diameter and varying in length from 20 inches to 5 feet according to the capacity of the mill. The surfaces of the cylinders are fluted or ribbed, the distance from rib to rib being about one-tenth of an inch. The rollers are mounted so that the distance between their surfaces can be adjusted. They are set so that they will break grains passing between them to from one-half to one-quarter their original size. They are made to revolve so that the parts of the surfaces between which the grains are nipped are travelling in the same direction. One roll revolves usually at about 350 revolutions per minute, the other at rather less than half that rate (Fig. 14). It is obvious from the above description that a grain of wheat falling from the hopper on to the surface of the moving rollers will be crushed or nipped between them, and that since the rollers are moving at different rates, it will at the same time be more or less torn apart. By altering the distance between the rollers and their respective speeds of revolution the relative amounts of nipping and tearing can be adjusted to suit varying conditions. [Illustration: Fig. 14. Break rolls. The large and small cog-wheels are the simplest device used to give the two rolls different speeds. The larger cog-wheel is driven by power and drives the smaller, of course at a much higher rate of revolution]